Hello,
Refer to this technote:
http://support.veritas.com/docs/271186
What you rae facing is a problem related to the inbuilt limitation of MAPI. Backup Exec uses Mapi interface to communicate with MS Exchange, the mapi session cannot handle more than 250 objects.
The solution provided by Miscrosoft is hence the only one applicable here if your case fufills all conditions specified in this technote.
NOTE : If we do not receive your reply within two business days, this post would be marked assumed answeredand would be moved toanswered questions pool.