In order to resolve this you can deduct the Time Off In Lieu (TOIL) from the user's profile and re-add this with an expiry date later than the date of the requested holiday.
Follow the steps below:
Click Access Button
then click Employee.
Open the relevant employee's record then select their Planner.
Select the planner settings option click the Add option next to TOIL.
Click the + icon to turn this into a - icon then input the relevant amount of TOIL.
Click Save then re-add the amount of TOIL you deducted into the box and set the expiry date.
Click Save then try to book the TOIL again.