Services suddenly stop working

Question

Hi,
I wrote a few custom services in Automator to drive the program iStopMotion (telling the program to take the next picture, delete the last picture, play the movie, etc.).  They work fine for a while and then... they just stop.  You can neither trigger them with their keyboard shortcuts, nor run them from the services menu (they appear there as normal, but clicking them has no effect).
This line shows up in the log whenever this happens:
4/29/13 10:15:47.504 AM iStopMotion[187]: NSTrackPersistentURLs: LSSharedFileListItemRemove() failed with error -50 on URL file://localhost/Users/stopmotion1/Documents/2013April29-36899.mov (/Users/stopmotion1/Documents/2013April29-36899.mov)
I've searched on that error and haven't turned up much.  Any ideas?

Answer 1

The application still works normally, so I can execute all the operations from within the application (using both its menus and its keyboard shortcuts).  It's just the services that aren't working.
A bit more info: 
1.  *Other* services still work, it's just the Automator-derived ones that stop working.  (For example, I can launch Text Edit and use the 'Capture Selection From Screen' service just fine.)
2.  The error that's recorded in the log isn't as consistent as I thought before.  For example, just now I got the following (which makes a bit more sense; at least it's Automator complaining about something):
4/29/13 3:05:10.710 PM com.apple.automator.xpc.workflowServiceRunner[207]: void workflow_service_runner_peer_handler(xpc_connection_t, xpc_object_t): Peer XPC handler received unexpected message error: Connection invalid
3.  Another weird thing:  After a restart, oftentimes the key commands for my services won't work (I just get an alert sound) until I go and manually click one of them from the Services menu.
At any rate, I have an identical Mac mini here, so I'll probably try to set all this up on it and see if the problem happens there, too.
Thanks for your input so far!