I had one instance of that problem a couple of weeks back whilst activating several users on the BES. I stopped all the services in the services section, did a restart on the domino console. Then restarted the BES NT services. Problem imediately went away. Obviously not the way to solve the problem....but it hasn't returned since. Since you rebooted, you could selectively stop and restart the services thru the services app section.
I don't believe that this is an access issue, since it only affects one user. You didn't mention if the SQL db is remote or local? If it is remote restart the SQL services. In my case, SQL is local. If you have enabled verbose logging, check the logs for other issues with this user. Check the "SYNC" logs...(one of them refers to syncing info)...chances are you may find the user has not synced entirely (especially the calendar stuff). Look at the entries for OTAFM and OTAC. If the OTAC reads...0X000000 the OTAC has not synced as yet. May need to resend service books.