diff --git a/Simulation/Aivika/IO/Resource/Preemption.hs b/Simulation/Aivika/IO/Resource/Preemption.hs
--- a/Simulation/Aivika/IO/Resource/Preemption.hs
+++ b/Simulation/Aivika/IO/Resource/Preemption.hs
@@ -21,6 +21,7 @@
 import Data.IORef
 import Data.Monoid
 
+import Simulation.Aivika.Trans.Exception
 import Simulation.Aivika.Trans.Ref.Base
 import Simulation.Aivika.Trans.DES
 import Simulation.Aivika.Trans.Template
@@ -72,12 +73,14 @@
     do let r = pointRun p
            t = pointTime p
        when (count < 0) $
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be negative: " ++
          "newResourceWithMaxCount."
        case maxCount of
          Just maxCount | count > maxCount ->
-           error $
+           throwComp $
+           SimulationRetry $
            "The resource count cannot be greater than " ++
            "its maximum value: newResourceWithMaxCount."
          _ ->
@@ -235,7 +238,8 @@
          then do invokeEvent p $ updateResourceUtilisationCount r (-1)
                  invokeEvent p $ releaseResource' r
                  invokeEvent p $ resumeCont c ()
-         else error $
+         else throwComp $
+              SimulationRetry
               "The resource was not acquired by this process: releaseResource"
 
   {-# INLINABLE usingResourceWithPriority #-}
@@ -245,7 +249,7 @@
 
   {-# INLINABLE incResourceCount #-}
   incResourceCount r n
-    | n < 0     = error "The increment cannot be negative: incResourceCount"
+    | n < 0     = throwEvent $ SimulationRetry "The increment cannot be negative: incResourceCount"
     | n == 0    = return ()
     | otherwise =
       do releaseResource' r
@@ -253,7 +257,7 @@
 
   {-# INLINABLE decResourceCount #-}
   decResourceCount r n
-    | n < 0     = error "The decrement cannot be negative: decResourceCount"
+    | n < 0     = throwEvent $ SimulationRetry "The decrement cannot be negative: decResourceCount"
     | n == 0    = return ()
     | otherwise =
       do decResourceCount' r
@@ -309,7 +313,8 @@
      let a' = a + 1
      case resourceMaxCount r of
        Just maxCount | a' > maxCount ->
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be greater than " ++
          "its maximum value: releaseResource'."
        _ ->
@@ -351,7 +356,8 @@
   do let t = pointTime p
      a <- liftIO $ readIORef (resourceCountRef r)
      when (a == 0) $
-       error $
+       throwComp $
+       SimulationRetry
        "The resource exceeded and its count is zero: decResourceCount'"
      f <- liftIO $ PQ.queueNull (resourceActingQueue r)
      unless f $
diff --git a/Simulation/Aivika/IO/Resource/Preemption/Base.hs b/Simulation/Aivika/IO/Resource/Preemption/Base.hs
--- a/Simulation/Aivika/IO/Resource/Preemption/Base.hs
+++ b/Simulation/Aivika/IO/Resource/Preemption/Base.hs
@@ -20,6 +20,7 @@
 import Data.Maybe
 import Data.IORef
 
+import Simulation.Aivika.Trans.Exception
 import Simulation.Aivika.Trans.Ref.Base
 import Simulation.Aivika.Trans.DES
 import Simulation.Aivika.Trans.Template
@@ -50,7 +51,8 @@
   newResource count =
     Simulation $ \r ->
     do when (count < 0) $
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be negative: " ++
          "newResource."
        countRef <- liftIO $ newIORef count
@@ -65,12 +67,14 @@
   newResourceWithMaxCount count maxCount =
     Simulation $ \r ->
     do when (count < 0) $
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be negative: " ++
          "newResourceWithMaxCount."
        case maxCount of
          Just maxCount | count > maxCount ->
-           error $
+           throwComp $
+           SimulationRetry $
            "The resource count cannot be greater than " ++
            "its maximum value: newResourceWithMaxCount."
          _ ->
@@ -134,7 +138,8 @@
        if f
          then do invokeEvent p $ releaseResource' r
                  invokeEvent p $ resumeCont c ()
-         else error $
+         else throwComp $
+              SimulationRetry
               "The resource was not acquired by this process: releaseResource"
                
   {-# INLINABLE usingResourceWithPriority #-}
@@ -144,7 +149,7 @@
 
   {-# INLINABLE incResourceCount #-}
   incResourceCount r n
-    | n < 0     = error "The increment cannot be negative: incResourceCount"
+    | n < 0     = throwEvent $ SimulationRetry "The increment cannot be negative: incResourceCount"
     | n == 0    = return ()
     | otherwise =
       do releaseResource' r
@@ -152,7 +157,7 @@
 
   {-# INLINABLE decResourceCount #-}
   decResourceCount r n
-    | n < 0     = error "The decrement cannot be negative: decResourceCount"
+    | n < 0     = throwEvent $ SimulationRetry "The decrement cannot be negative: decResourceCount"
     | n == 0    = return ()
     | otherwise =
       do decResourceCount' r
@@ -202,7 +207,8 @@
      let a' = a + 1
      case resourceMaxCount r of
        Just maxCount | a' > maxCount ->
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be greater than " ++
          "its maximum value: releaseResource'."
        _ ->
@@ -236,7 +242,8 @@
   Event $ \p ->
   do a <- liftIO $ readIORef (resourceCountRef r)
      when (a == 0) $
-       error $
+       throwComp $
+       SimulationRetry
        "The resource exceeded and its count is zero: decResourceCount'"
      f <- liftIO $ PQ.queueNull (resourceActingQueue r)
      unless f $
diff --git a/Simulation/Aivika/Trans/Event.hs b/Simulation/Aivika/Trans/Event.hs
--- a/Simulation/Aivika/Trans/Event.hs
+++ b/Simulation/Aivika/Trans/Event.hs
@@ -37,6 +37,8 @@
         memoEventInTime,
         -- * Disposable
         DisposableEvent(..),
+        -- * Retrying Computation
+        retryEvent,
         -- * Debugging
         traceEvent) where
 
diff --git a/Simulation/Aivika/Trans/Internal/Cont.hs b/Simulation/Aivika/Trans/Internal/Cont.hs
--- a/Simulation/Aivika/Trans/Internal/Cont.hs
+++ b/Simulation/Aivika/Trans/Internal/Cont.hs
@@ -830,7 +830,15 @@
      if not f
        then invokeEvent p $
             enqueueEvent (pointTime p) $
-            resumeCont c a
+            Event $ \p ->
+            do f <- invokeEvent p $
+                    contPreemptionBegun $
+                    contId $ contAux c
+               if not f
+                 then invokeEvent p $
+                      resumeCont c a
+                 else invokeEvent p $
+                      sleepCont c a
        else invokeEvent p $
             sleepCont c a
 
diff --git a/Simulation/Aivika/Trans/Internal/Event.hs b/Simulation/Aivika/Trans/Internal/Event.hs
--- a/Simulation/Aivika/Trans/Internal/Event.hs
+++ b/Simulation/Aivika/Trans/Internal/Event.hs
@@ -41,6 +41,8 @@
         memoEventInTime,
         -- * Disposable
         DisposableEvent(..),
+        -- * Retrying Computation
+        retryEvent,
         -- * Debugging
         traceEvent) where
 
@@ -296,6 +298,11 @@
 
   {-# INLINE mappend #-}
   mappend (DisposableEvent x) (DisposableEvent y) = DisposableEvent $ x >> y
+
+-- | Retry the current computation as possible, using the specified argument
+-- as a 'SimulationRetry' exception message in case of failure.
+retryEvent :: MonadException m => String -> Event m a
+retryEvent message = throwEvent $ SimulationRetry message
 
 -- | Show the debug message with the current simulation time.
 traceEvent :: MonadDES m => String -> Event m a -> Event m a
diff --git a/Simulation/Aivika/Trans/Internal/Process.hs b/Simulation/Aivika/Trans/Internal/Process.hs
--- a/Simulation/Aivika/Trans/Internal/Process.hs
+++ b/Simulation/Aivika/Trans/Internal/Process.hs
@@ -85,6 +85,8 @@
         memoProcess,
         -- * Never Ending Process
         neverProcess,
+        -- * Retrying Computation
+        retryProcess,
         -- * Debugging
         traceProcess) where
 
@@ -762,6 +764,11 @@
   let signal = processCancelling pid
   in handleSignal_ signal $ \_ ->
      resumeCont c $ error "It must never be computed: neverProcess"
+
+-- | Retry the current computation as possible, using the specified argument
+-- as a 'SimulationRetry' exception message in case of failure.
+retryProcess :: MonadDES m => String -> Process m a
+retryProcess = liftEvent . retryEvent
 
 -- | Show the debug message with the current simulation time.
 traceProcess :: MonadDES m => String -> Process m a -> Process m a
diff --git a/Simulation/Aivika/Trans/Internal/Simulation.hs b/Simulation/Aivika/Trans/Internal/Simulation.hs
--- a/Simulation/Aivika/Trans/Internal/Simulation.hs
+++ b/Simulation/Aivika/Trans/Internal/Simulation.hs
@@ -26,7 +26,8 @@
         throwSimulation,
         -- * Exceptions
         SimulationException(..),
-        SimulationAbort(..)) where
+        SimulationAbort(..),
+        SimulationRetry(..)) where
 
 import Control.Exception
 import Control.Monad
@@ -42,7 +43,7 @@
 import Simulation.Aivika.Trans.Internal.Specs
 import Simulation.Aivika.Trans.Internal.Parameter
 
-import Simulation.Aivika.Simulation (SimulationException, SimulationAbort)
+import Simulation.Aivika.Simulation (SimulationException(..), SimulationAbort(..), SimulationRetry(..))
 
 instance Monad m => Monad (Simulation m) where
 
diff --git a/Simulation/Aivika/Trans/Process.hs b/Simulation/Aivika/Trans/Process.hs
--- a/Simulation/Aivika/Trans/Process.hs
+++ b/Simulation/Aivika/Trans/Process.hs
@@ -83,6 +83,8 @@
         memoProcess,
         -- * Never Ending Process
         neverProcess,
+        -- * Retrying Computation
+        retryProcess,
         -- * Debugging
         traceProcess) where
 
diff --git a/Simulation/Aivika/Trans/Resource.hs b/Simulation/Aivika/Trans/Resource.hs
--- a/Simulation/Aivika/Trans/Resource.hs
+++ b/Simulation/Aivika/Trans/Resource.hs
@@ -72,6 +72,7 @@
 import Control.Monad.Trans
 import Control.Exception
 
+import Simulation.Aivika.Trans.Exception
 import Simulation.Aivika.Trans.Ref.Base
 import Simulation.Aivika.Trans.DES
 import Simulation.Aivika.Trans.Internal.Specs
@@ -228,12 +229,14 @@
   do let r = pointRun p
          t = pointTime p
      when (count < 0) $
-       error $
+       throwComp $
+       SimulationRetry $
        "The resource count cannot be negative: " ++
        "newResourceWithMaxCount."
      case maxCount of
        Just maxCount | count > maxCount ->
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be greater than " ++
          "its maximum value: newResourceWithMaxCount."
        _ ->
@@ -459,7 +462,8 @@
      let a' = a + 1
      case resourceMaxCount r of
        Just maxCount | a' > maxCount ->
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be greater than " ++
          "its maximum value: releaseResource'."
        _ ->
@@ -550,7 +554,7 @@
                     -> Event m ()
 {-# INLINABLE incResourceCount #-}
 incResourceCount r n
-  | n < 0     = error "The increment cannot be negative: incResourceCount"
+  | n < 0     = throwEvent $ SimulationRetry "The increment cannot be negative: incResourceCount"
   | n == 0    = return ()
   | otherwise =
     do releaseResource' r
@@ -566,7 +570,7 @@
                     -> Process m ()
 {-# INLINABLE decResourceCount #-}
 decResourceCount r n
-  | n < 0     = error "The decrement cannot be negative: decResourceCount"
+  | n < 0     = throwProcess $ SimulationRetry "The decrement cannot be negative: decResourceCount"
   | n == 0    = return ()
   | otherwise =
     do decResourceCount' r
diff --git a/Simulation/Aivika/Trans/Resource/Base.hs b/Simulation/Aivika/Trans/Resource/Base.hs
--- a/Simulation/Aivika/Trans/Resource/Base.hs
+++ b/Simulation/Aivika/Trans/Resource/Base.hs
@@ -57,6 +57,7 @@
 import Control.Monad.Trans
 import Control.Exception
 
+import Simulation.Aivika.Trans.Exception
 import Simulation.Aivika.Trans.Ref.Base
 import Simulation.Aivika.Trans.DES
 import Simulation.Aivika.Trans.Internal.Specs
@@ -180,7 +181,8 @@
 newResource s count =
   Simulation $ \r ->
   do when (count < 0) $
-       error $
+       throwComp $
+       SimulationRetry $
        "The resource count cannot be negative: " ++
        "newResource."
      countRef <- invokeSimulation r $ newRef count
@@ -204,12 +206,14 @@
 newResourceWithMaxCount s count maxCount =
   Simulation $ \r ->
   do when (count < 0) $
-       error $
+       throwComp $
+       SimulationRetry $
        "The resource count cannot be negative: " ++
        "newResourceWithMaxCount."
      case maxCount of
        Just maxCount | count > maxCount ->
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be greater than " ++
          "its maximum value: newResourceWithMaxCount."
        _ ->
@@ -306,7 +310,8 @@
      let a' = a + 1
      case resourceMaxCount r of
        Just maxCount | a' > maxCount ->
-         error $
+         throwComp $
+         SimulationRetry $
          "The resource count cannot be greater than " ++
          "its maximum value: releaseResourceWithinEvent."
        _ ->
@@ -382,7 +387,7 @@
                     -> Event m ()
 {-# INLINABLE incResourceCount #-}
 incResourceCount r n
-  | n < 0     = error "The increment cannot be negative: incResourceCount"
+  | n < 0     = throwEvent $ SimulationRetry "The increment cannot be negative: incResourceCount"
   | n == 0    = return ()
   | otherwise =
     do releaseResourceWithinEvent r
@@ -398,7 +403,7 @@
                     -> Process m ()
 {-# INLINABLE decResourceCount #-}
 decResourceCount r n
-  | n < 0     = error "The decrement cannot be negative: decResourceCount"
+  | n < 0     = throwProcess $ SimulationRetry "The decrement cannot be negative: decResourceCount"
   | n == 0    = return ()
   | otherwise =
     do requestResource r
diff --git a/Simulation/Aivika/Trans/Simulation.hs b/Simulation/Aivika/Trans/Simulation.hs
--- a/Simulation/Aivika/Trans/Simulation.hs
+++ b/Simulation/Aivika/Trans/Simulation.hs
@@ -22,6 +22,7 @@
         throwSimulation,
         -- * Exceptions
         SimulationException(..),
-        SimulationAbort(..)) where
+        SimulationAbort(..),
+        SimulationRetry(..)) where
 
 import Simulation.Aivika.Trans.Internal.Simulation
diff --git a/aivika-transformers.cabal b/aivika-transformers.cabal
--- a/aivika-transformers.cabal
+++ b/aivika-transformers.cabal
@@ -1,5 +1,5 @@
 name:            aivika-transformers
-version:         4.3.3
+version:         4.3.4
 synopsis:        Transformers for the Aivika simulation library
 description:
     This package is a generalization of the Aivika [1] simulation library
@@ -144,7 +144,7 @@
                      containers >= 0.4.0.0,
                      random >= 1.0.0.3,
                      vector >= 0.10.0.1,
-                     aivika >= 4.3.1
+                     aivika >= 4.3.4
 
     other-extensions:   FlexibleContexts,
                         FlexibleInstances,