Time card error: "The earned date of the compensatory time transaction must be..."

Summary: One of our employee's time cards is throwing this error whenever we try to Save and Close it (or try to make any adjustments):

"The earned date of the compensatory time transaction must be between the plan enrollment start and end dates."

Their Compensatory plan enrollment is effective as of 9/15. I've adjusted the enrollment date to 9/13 and it throws the same error. None of their other time cards throw this error. How do we fix this to be able to update the time card?