The requirement is to prevent users from tracking time to projects / tasks that are closed for time entry.
This occurs only when the task has been added to a timesheet prior to time tracking being turned off, and then submitted after time tracking is turned off.
We are using CA PPM v184.108.40.206 On Premise. Is there any way to prevent this?
There is no OOB way to prevent this. Your best bet is to have a workflow that runs when the timesheet is submitted that will return the timesheet with a message telling the user that the closed task should not be used.