Barracuda ERROR: Could not connect to Barracuda Backup Agent on when backing up 'Agent' on server

Event ID 35: The shadow copies of volume F: were aborted because the shadow copy storage failed to grow.

Situation: The client is running Barracuda backup to back up Exchange. It stops after backing up 4 hours with this error: Could not connect to Barracuda Backup Agent on when backing up 'Agent' on server. Also the emails were stuck in Exchange queue. Troubleshooting: We found error in the Event Viewer:

Log Name: System
Source: volsnap
Date: 1/5/2012 10:54:41 PM
Event ID: 35
Task Category: None
Level: Error
Keywords: Classic
User: N/A
Computer: EXCH-MAIL01
Description:
The shadow copies of volume F: were aborted because the shadow copy storage failed to grow.

The Exchange backup hasn't been backing up for one month and the log drive keeps a lot old log files. That eats a lot spaces. When the Barracuda Backs up the Exchange, it uses some spaces. The resolution is adding more space or delete some files in log drive. After we have over 10% free space, the backup works fine.

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