“End call Failed – Exception” when attempting to end a call while on hold should be more meaningful

When an agent has a caller on hold and attempts to end the call, the agent gets a "End call Failed – Exception" error message. This error message does not make it clear to the user what needs to be done to end the call. The error message should read "Please take caller off hold before ending the call" or something similar. This may be specific to implementations on the Aspect phone system.