Exchange Backups failing

Team,

Backup Version :Symantec Backup Exec verison 2010 R3.

Type of Backup : Exchnage Backup Issue

Tape Library Model : Quantum I 80

Exchnage Backups are getting failed with the following error, when it is configured to the tape library.

e00002fe - Cannot log on to MAPI with the specified credentials. Review the resource credentials for the job, and then run the job again.

But if the same backup is configured to the backup to disk then it is completing successfull.

Can you pelase help on this issue & help in resolving it.

Note : Remaining all other backups are running successfully on the same library

let me know if you need any more information
 

Regards,

Vamsi