This issue has been found to be caused when the absence type the absence is linked to is made inactive in lookup administration.
You can check this if you have the required permissions by following the simple steps:
Log in to CallConfirmLive!
Click System, then click Lookup Administration.
Expand the Absence Type folder.
Locate the Absence Type in use with your absence and double click it to open the details.
Ensure a tick is shown next to Active. If the lookup is not active, make it active, end your absence, and then make it inactive again.