I also tried to use an E51 with BBC as an alternative for my BB 8320 and I got into a similar mess - none was working properly until I phoned my service provider and they re-enabled the BIS service on my 8320. Sorry, I don't know about BES. From what I understood, you can only have one device registered with BB service at a time. To change the device, you have to change both the device serial and PIN, which for me turned out to be impossible.