Inactive Users: If the extension has a gray bubble you either need to activate it to disable it then delete it, or contact support to have it deleted. Support can ONLY delete a User if there is NO Digital Line (DL) attached...this is due to contract reasons. If there is a DL attached then you must contact your sales representative.
* (DL meaning a device + a number)
Users > find the extension> then Disable it
After the extension is disabled, it can be deleted.