I hope you aren't trying to do this in a 'headless' state, with no user logged in. FMP doesn't run very well without a GUI. For example you can't access a menu item without a menu. I'm not even sure you can launch the FMP Application without a User logged in.
Also, the FMS account does NOT have access to the User's folders.
wild guess: target file OS level permissions?
I am thinking along the lines of pushing a backup to a locally attached drive; if the target directory does not have fmserver ownership the schedule path will be invalid...
Just because an FMP file can execute shell scripts/apple scripts, does not necessarily mean FMS schedule can ( under same conditions). As chocoholic was indicating (maybe) by: <<FMS account does NOT have access to the User's folders>>
As I said, just a guess.
No there is a user logged in and that user is the one desgnated to run the script - not using the FMS account
However I have downloaded Cronixx and that that seems to work fine.
Beginning in Mac OS X v10.4, the preferred way to add a timed job is to use a launchd timed job. But small task and it works...