Hi Mike
The other thing to check is if the signatures in the SQL database are correct if they are then approach ManageEngine on how to flush the cache and rebuild from the SQL database.
Playing around with the Cache Folder is probably not a good idea unless ManageEngine has told you how it works.
I would have suggested shutting down the ServiceDesk and restarting it and see if that rebuilds the cache.
The other thing to check is if the signatures in the SQL database are correct if they are then approach ManageEngine on how to flush the cache and rebuild from the SQL database.
Would be nice if it was documented :D