Tasks don't have anything to do with group policy, unless you asign them through GP, then that has nothing to do with the running. If the .job file is local, it monitors the system clock, and an event is triggered at the specified time. It it possible, but unlikely that the .job files have been corrupted as such. What I suggest you try.
First thing is a test.
Copy all the job files to another folder. Delete them from the scheduled tasks folder. Reboot.
create a new task, with the scheduled task wizzard, and just set it to start notepad in like 2 minutes. Just to make sure your task registration is working correctly. If notepad or whatever, launches, then your system is working fine. You either have a problem with your tasks registrations, or your actual .job files themselves.
Copy the job files one by one back to the scheduled tasks folder. When each one is created, it is registered as a new task, and creates a time stamp marker for it. It may be that the registrations for the tasks had been got at by any one of many possible reasons.
Also, if that doesn't work, remove the tasks again. Try recreating, again, through the wizzard one of your specified tasks, just as it should have been in the old ones. This may help if for some bizzar reason, your task files have been corrupted.
Hope this Helps.
Neil J Cotton
njc Information Systems
Systems Consultant