Thanks for all your replies and help. And apologize for not keeping up with my own thread
But the issue with the two specific users I had problems at the time with was due to the local PST file use, as they are traveling users. But we've still had some issues with the newer 8700 series devices with some other users that leave their mailbox data on the server, so I think its something to do with some incompatibility between the version of BES we have and the exchange or the newer devices...
Thanks again