In IP Manager Assistant (IPMA) proxy mode, the phone of the manager and the assistant console work properly, and an assistant can log on to the phone and be seen online by the manager. But, when the assistant tries to access the IPMA service, the IP phone displays the HTTP ERROR  error message.
All of the other services run fine.
The appearance of the HTTP Error  is a normal behavior when an assistant user tries to access the IPMA Phone Service on the assistant phone, because assistants do not have access to this service. If an assistant is subscribed to that service, complete these steps: