Hi Anthony,
I have tried below work arounds from CA Support and nothing worked.
1.Going back / refreshing the page and navigating from beginning.
2.Clearing the Browser caches.
3.Clearing the App Caches/Groups.
4. CA Support team has "RESTARTED" the application services. Still issue not resolved.
Below Worked.
Using XOG the tasks from that timesheet were removed, now user was able to Add Hours and Timesheets got Posted now.
Hope this may helps you.
Thanks.