MS Small Busines Server 2003 R2
Exchange 2003
BES 4.1

The calender is only syncing from the server to the blackberry, not both ways. Email and contacts seem to be syncing both ways. Any ideas?

Welcome to the forums!

Most likely your cdo.dll version on your BES is older than you Exchange Server. Have you applied all of the Exchange service packs to your BES that you've done to your Exchange server? Search the forums for Exchange one way calendar