You probably need to upgrade your backup exec version to support Exchange 2007 SP1. I would get on the phone with Symantec and ask for their support on this immediately.
<a href=”http://seer.entsupport.symantec.com/docs/289970.htm”>From Symantec </a>
“The above error is reported if the version of the ESE.DLL on the Backup Exec server is different from the one on the Exchange 2007 server. This occurs in the event that the Exchange 2007 server has been patched to recent updates like Service Packs/ Rollup Patches for Exchange but the same Service Packs/Rollup Patches have not been applied to the Exchange 2007 Management Tools installed on the Backup Exec server. “