Error while approving Timesheet: TimeOff that need booking can not be added as ad-hoc TimeOff

Scenario:
The following error shows up when an approver is trying to approve a timesheet: TimeOff that need booking can not be added as ad-hoc TimeOff.

Cause:
Booking required option was enabled for a time off type after it was added in the timesheet that is waiting for approval.

Resolution:
In order to complete the approval of the timesheet, follow the listed steps.

• Reopen the affected timesheet.
• Check for the timeoff type that is added in the timesheet.
• Disable the booking required option for that particular timeoff type.
• You should be able to approve the timesheet.
• Once the timesheet is approved, you can enable the booking required option for that time off type.