Hi All, just to update this is now working. I believe it was the BES Admin permissions on the databases when we migrated over to 2010 (even though the same BES Admin account was servicing BES 4 accounts fine from 2010, and for Exchange 2010 users).
I am going to speak to a techie from our carrier later, and see if we can spot what it was, if so I will post to let you know.
Thanks everyone for the help, in particular Hannah814 and fadmin!
Cheers
Dom