Calendar Entries will not sync to Outlook

[markodrummer]

Hi Everyone - i know there are quite a few threads already on this issue but I have had no luck resolving this issue.

Here some background info:
Running 1 BES 5.0 MR2 Server - Windows 2003 R2
Multiple Exchange Servers - all running Exchange 2003 on Windows 2003 R2

Ever since upgrading our BES Server from 4.0.7 to 5.0 all users of only one of our exchange servers cannot successfully sync appointments from their BB to Outlook.

Heres what I have checked thus far:
- CDO.DLL and MAPI32.DLL files are up-to-date and the same across the board on all EXCHANGE servers and BES server
- BESAdmin account has full Send As, Receive As, Information Store view privileges on All servers, databases and public folders. All permissions are inherited and are exactly the same across all our EXCHANGE servers
- Anonymous Login has Read access to all users calendars
- MAPI has not been disabled in the forest (checked via adsiedit.msc)
- Servers are all patched and up-to-date

The following is logged in the MAGT log:

CDO initializing failure in CDO helper 054940E8 (2)
[30002] (02/03 02:23:11.187):{0x25F8} Server = [servername], Mailbox = /o=Blah/ou=First Administrative Group/cn=Recipients/cn=username Description = You do not have permission to log on. [Microsoft Exchange Server Information Store - [MAPI_E_FAILONEPROVIDER(8004011D)]]
[30180] (02/03 02:23:11.187):{0x25F8} {username} CDOCalendar::Initialize - Error in call m_spCalendarFolder = m_spCDOSession->GetDefaultFolder

Any help would be appreciated!
Mark