You might receive this message you try to cancel a leave after it has passed the leave date 

This message essentially means submitter is trying to cancel a leave on the same day of the leave date or after that.

Example, he applied at 25/6 to on leave at 1/7 to 2/7. Then he can only cancel it prior to 1/7. System will show this message if it's cancelling at 1/7 onwards. Else user will be able to cancel leave that's approve after few weeks the leave is taken, and the balance will be incremented back.