Taken from the Qlikview Server Reference Manual
"To delete an assigned user, thus freeing a Document CAL, click on the Delete button ( ). If the CAL
has not been in use for the last 24 hours, it will be deleted immediately. If the CAL is currently being used
or has recently been used, it will be marked for deletion, and not allow new sessions for user access
through this CAL, but will still occupy an allocated CAL until the Quarantine time ends. During this
period, you may undelete by clicking the Restore button ( ). After the quarantine period, you may
delete the entry manually (by clicking on the Delete button), or restart the QVS service"