diff --git a/cloudi.cabal b/cloudi.cabal
--- a/cloudi.cabal
+++ b/cloudi.cabal
@@ -1,5 +1,5 @@
 name:                cloudi
-version:             2.0.0
+version:             2.0.1
 synopsis:            Haskell CloudI API
 description:         Haskell CloudI API (see https://cloudi.org for more details)
 homepage:            https://github.com/CloudI/cloudi_api_haskell
diff --git a/src/Foreign/CloudI.hs b/src/Foreign/CloudI.hs
--- a/src/Foreign/CloudI.hs
+++ b/src/Foreign/CloudI.hs
@@ -42,6 +42,7 @@
     , messageDecodingError
     , terminateError
     , Exception
+    , FatalError
     , Result
     , api
     , threadCount
@@ -101,6 +102,8 @@
 import qualified System.IO.Error as SysIOErr
 import qualified System.IO.Unsafe as Unsafe
 import qualified System.Posix.Env as POSIX (getEnv)
+import qualified System.Posix.Process as POSIX (exitImmediately)
+import qualified System.Exit as Exit
 type Array = IArray.Array
 type Builder = Builder.Builder
 type ByteString = ByteString.ByteString
@@ -110,6 +113,10 @@
 type Map = Map.Map
 type RequestType = Instance.RequestType
 type SomeException = Exception.SomeException
+type SomeAsyncException = Exception.SomeAsyncException
+type AsyncException = Exception.AsyncException
+type AssertionFailed = Exception.AssertionFailed
+type ExitCode = Exit.ExitCode
 type Source = Instance.Source
 type ThreadId = Concurrent.ThreadId
 type Word32 = Word.Word32
@@ -165,6 +172,13 @@
 
 instance Typeable s => Exception.Exception (Exception s)
 
+data FatalError = FatalError
+
+instance Exception.Exception FatalError
+
+instance Show FatalError where
+    showsPrec _ FatalError = showString "FatalError"
+
 printException :: String -> IO ()
 printException str =
     SysIO.hPutStrLn SysIO.stderr ("Exception: " ++ str)
@@ -219,7 +233,9 @@
                             return $ Left err
                         Right (_, api1) ->
                             return $ Right api1
-        (_, _) ->
+        (_, _) -> do
+            SysIO.hPutStrLn SysIO.stderr
+                "CloudI service execution must occur in CloudI"
             return $ Left invalidInputError
 
 -- | returns the thread count from the service configuration
@@ -636,6 +652,26 @@
 nullResponse _ _ _ _ _ _ _ _ _ state api0 =
     return $ Instance.Null (state, api0)
 
+callbackExceptionFatal :: SomeException -> IO ()
+callbackExceptionFatal e = do
+    printException $ show e
+    POSIX.exitImmediately (Exit.ExitFailure 1)
+
+callbackException :: SomeException -> IO ()
+callbackException e
+    | Just _ <- (Exception.fromException e :: Maybe AsyncException) =
+        callbackExceptionFatal e
+    | Just _ <- (Exception.fromException e :: Maybe SomeAsyncException) =
+        callbackExceptionFatal e
+    | Just _ <- (Exception.fromException e :: Maybe AssertionFailed) =
+        callbackExceptionFatal e
+    | Just _ <- (Exception.fromException e :: Maybe FatalError) =
+        callbackExceptionFatal e
+    | Just exitCode <- (Exception.fromException e :: Maybe ExitCode) =
+        POSIX.exitImmediately exitCode
+    | otherwise =
+        printException $ show e
+
 callback :: Typeable s => Instance.T s ->
     (RequestType, ByteString, ByteString, ByteString, ByteString,
      Int, Int, ByteString, Source) -> IO (Result (Instance.T s))
@@ -650,7 +686,7 @@
             Just functionQueue ->
                 let f = Sequence.index functionQueue 0
                     functionQueueNew = (Sequence.|>)
-                        (Sequence.drop 0 functionQueue) f
+                        (Sequence.drop 1 functionQueue) f
                 in
                 (f, Map.insert pattern functionQueueNew callbacks)
         api1 = api0{Instance.callbacks = callbacksNew}
@@ -720,7 +756,7 @@
                     return $ ReturnI (empty, empty, v0, v1)
     callbackResultType <- case callbackResultValue of
         Left exception -> do
-            printException $ show (exception :: Exception.SomeException)
+            callbackException exception
             return $ ReturnI (empty, empty, state, api1)
         Right callbackResult ->
             return $ callbackResult
diff --git a/src/Foreign/CloudI/Instance.hs b/src/Foreign/CloudI/Instance.hs
--- a/src/Foreign/CloudI/Instance.hs
+++ b/src/Foreign/CloudI/Instance.hs
@@ -267,7 +267,7 @@
             Nothing ->
                 error "callbacks empty"
             Just functionQueue ->
-                let functionQueueNew = Sequence.drop 0 functionQueue in
+                let functionQueueNew = Sequence.drop 1 functionQueue in
                 if Sequence.null functionQueueNew then
                     Map.delete key callbacks0
                 else