OK gents I upgraded from BES for Exchange 3.6.7 to 4.0 SP5a today. My main problem is that calendar appointments keyed on the BB 7520 are not getting replicated back to Outlook. Our Exchange environment is 2003 SP2.

I did receive an error during the upgrade to 4.0:
" Warning: Unable to load CDO.DLL "

I searched for this file and found it in c:\program files\exchsrvr\bin version 6.5.7638.2 which is consistant with my Exchange 2003 SP2 server.

I read an article about this file also needing to be in c:\windows\system32. So I copied it there and regsvr32ed it. Rebooted, but still calendar sync is only one way.

Also, I have performed the following several times:
1) Kill the user on the BES, wait for BB7520 to reset.
2) Remove user from BES.
3) Add the user back to BES.
4) Enterprise Activate on the BB7520.
Confirming that default Policy Status is "Applied Successfully"

Also, wireless calendar sync is on, on the BB7520.

What can I try next? Thank you all.

2 things that will cause Calendar from handheld to exchange to fail.
CDO & Permissions.
You said that you just upgraded. Did you use your BlackBerry service account? Verify the BlackBerry services are starting the BESAdmin or whatever your BlackBerry service account name is (NON DOMAIN ADMIN)

Or

Stop all BlackBerry Services.
Unregister CDO.dll from the bin directory.
Register cdo.dll and restart the services.

Thank you RIM-BBTECH.

I tried what you mentioned but had some unexpected results.

I finally got in touch with RIM and they had me remove from Domain Admins just as you said, but also I had to add Receive As and Send As permissions for BESAdmin in Exchange.

All is working now. Thanks a ton for getting me going in the right direction.