What version of cdo.dll do you have on the BES? Check the MAGT to see which one is registered, just search for cdo.dll from the top of the log down. You will see cdo.dll and MAPI32.dll listed. Also check that permissions are set correctly.
This issue is almost always cdo.dll or permissions, unless something is really messed up and those are extremely rare cases.
Search the
BlackBerry Technical Solution Center for "one way calendar" and you should find RIM's article about this issue as well.