The error is telling you that the UPS_Service session variable is not set at the top of the switch statement. If the code to set the session variable occurs before this then the session variable is not being set.
Did you put this at the top of the confirm page? Have you tried using the session variable that is set in this code anywhere else on the site? So long as that session variable is present and it has been set to the value of the posted service type it will work in the switch statement.