Backup Exec 2010 R3 - Error 0xe0001904

Hi,

I'm running Backup Exec 2010 R3 on SBS 2011 Standard.

I've set the backup with a full backup every Saturday and incremental from Monday to Friday. Every backup gets written in the specific folder of the day: i.e. Monday backup gets written in a Monday folder on my NAS, Tuesday in Tuesday folder and so. Could this cause errors?

While the full backup works without any problems, I'm getting the following error on all incremental backups:

Final error: 0xe0001904 - A failure occurred querying the Writer status.  Writer Name: Exchange Server, Writer ID: {76FE1AC4-15F7-4BCD-987E-8E1ACB462FB7}, Last error: The VSS Writer failed, but the operation can be retried (0x800423f3), State: Failed during prepare snapshot operation (8).
Final error category: Security Errors

For additional information regarding this error refer to link V-79-57344-6404

Backup
V-79-57344-6404 - AOFO: Initialization failure on: "\\SERVER\Microsoft Information Store\Mailbox Database". Advanced Open File Option used: Microsoft Volume Shadow Copy Service (VSS).

Snapshot provider error (0xE0001904): A failure occurred querying the Writer status.  Writer Name: Exchange Server, Writer ID: {76FE1AC4-15F7-4BCD-987E-8E1ACB462FB7}, Last error: The VSS Writer failed, but the operation can be retried (0x800423f3), State: Failed during prepare snapshot operation (8).

Check the Windows Event Viewer for details.

V-79-57344-6404 - AOFO: Initialization failure on: "\\SERVER\Microsoft Information Store\Public Folder Database 0440807651". Advanced Open File Option used: Microsoft Volume Shadow Copy Service (VSS).

Snapshot provider error (0xE0001904): A failure occurred querying the Writer status.  Writer Name: Exchange Server, Writer ID: {76FE1AC4-15F7-4BCD-987E-8E1ACB462FB7}, Last error: The VSS Writer failed, but the operation can be retried (0x800423f3), State: Failed during prepare snapshot operation (8).

Check the Windows Event Viewer for details.

Backup- C:
The .DR file that is required for Intelligent Disaster Recovery is not updated.

Backup- System?State
The .DR file that is required for Intelligent Disaster Recovery is not updated

Since I'm anything but an IT guru I've compared the differences between the settings in the full and the incremental backups and couldn't find anything odd.

I'd be very greatful for any help