This is probably the same question as NTBackup (on WS2k3) fails to backup remote server (WS2k8R2) with " Error: is not a valid drive, or you do not have access." but I have more detail.
I have a Windows Server 2003 machine with a Scheduled Task set to back up the system to a share on another machine. The scheduled task is configured to run as Domain Admin.
The command line is:
ntbackup backup systemstate "@C:\FullBackup.bks" /J "Even Week Backup Job" /F "\\machinename\sharename\ServerBackup_Even.bkf" /L:s /M Normal /SNAP:on
When run, the backup log shows:
Backup Status Operation: Backup Active backup destination: File Media name: "ServerBackup_Even.bkf created 2/1/2013 at 4:15 PM" Volume shadow copy creation: Attempt 1. Backup (via shadow copy) of "C: " Backup set #1 on media #1 Backup description: "Set created 2/1/2013 at 4:15 PM" Media name: "ServerBackup_Even.bkf created 2/1/2013 at 4:15 PM" Backup Type: Normal Backup started on 2/1/2013 at 4:18 PM. Error: The device reported an error on a request to write data to media. Error reported: Invalid command. There may be a hardware or media problem. Please check the system event log for relevant failures. The operation was ended. Backup completed on 2/1/2013 at 4:53 PM. Directories: 5383 Files: 46137 Bytes: 10,180,447,047 Time: 34 minutes and 48 seconds Error: C: is not a valid drive, or you do not have access. Error: An inconsistency was encountered in the requested backup file. ---------------------- The operation did not successfully complete. ----------------------
Here's the kicker: when I log on interactively to the server (with the same account that the task runs under) and kick off the scheduled task, it completes successfully. If I log on and start the task, then log off of my interactive session, the backup fails when I log off.