Backing up Microsoft Information Store with Symantec Backup Exec 12.5

Hi,

Backing up Microsoft Information Store getting failed on the below error:

Backup- \\myserver\Microsoft Information Store\First Storage Group Database  was not found, or could not be accessed.
Database  was not found, or could not be accessed.

The backup job backs the data to NAS. This was running fine earlier, but for past few weeks getting failed continuously. The rest of the data are backed up correctly but fails only on MIS.

Have checked with the job selection and it is correct. The job runs under administrator privileges. Have also tried backing up MIS alone separately, even then its getting failed.

But another job that backs up the same (Microsoft Information Store) to tape goes fine.

Any solutions?

Thanks