Can_not_drop_unused_file.mdwn

I have encrypted directory remote on a usb drive over time it accumulated some unused files. I would like to drop them running,

    git annex --unused --from external

returns a list of unused files when I try to drop them with,


    git annex dropunused --force --from external 1-XX

I get,

    dropunused XX (from external...) failed

I can not seem to get rid of these files.