Originally Posted by Ebop
Can you confirm that the reason is correct and if I copy the dll from our mail server to BES, re-register and restart BES services - that this will resolve the problem?
Should do the trick but also check your CDO.dlls are the same while you are about it. Also, while a services restart should work, I find more often than not that a change like this ends up needing a BES restart.
This might be a good chance to ensure that you have all the required hotfixes etc in place on the Exch servers and BESs (as they got out of sync) as you have to schedule downtime for this anyway. I have seen other causes of this so this might not be the fix but needs to be done as step one for sure.