Why does my Acronis backup keep failing?

I'm using Aconis True Image Workstation 10.  I've created a backup job that should backup my entire HD to a network location.  When entering the file location for the backup archive I choose the UNC not a drive mapping.  This computer is a member of a domain.  I've pasted the error log below.  The operating system is Windows XP Pro.  The destination is the server.  The folder where the backup is being stored, this user has full permission to that folder. Thanks in advance.

1    Information    5/18/2011 12:00:05 AM    Priority changed to Low.
2    Information    5/18/2011 12:00:05 AM    Analyzing partition '0-0'...
3    Information    5/18/2011 12:00:06 AM    Analyzing partition 'C:'...
4    Information    5/18/2011 12:00:06 AM    Analyzing partition 'C:'...
5    Information    5/18/2011 12:00:06 AM    Create Full Backup
From:      Disk '1'
To file:      "file://server\wrkstation_backups\Roy\Archive(2)_2011_05_18_00_00_04_641D.TIB"
Compression:      Normal
Exclude:      Files matching mask
Match criterion:      C:\Documents and Settings\All Users\Application Data\Acronis\BackupAndRecovery\MMS\Temp\acrFCE9.tmp,

6    Information    5/18/2011 12:00:06 AM    Pending operation 147 started: 'Creating partition image'.
7    Information    5/18/2011 12:00:08 AM    Locking partition C:...
8    Error    5/18/2011 12:00:12 AM    Operation with partition '0-0' was terminated.
Details:
Failed to create volume snapshot.

    Error code: 0x70021
    Tag: 0xA5695862AAF8E63A
Failed to start creating the volume snapshot.

    Error code: 0x10C442
    Tag: 0x14181C22EF45B04E
The device is not ready

    Error code: 0xFFF0
    code = 2,147,942,421 (0x80070015)
    Tag: 0xBD28FDBD64EDB8BC
Additional info:
--------------------
Error code: 502
Module: 1
LineInfo: a164035b3ff39281
Fields:
Message: Operation with partition '0-0' was terminated.
Details:
Failed to create volume snapshot.

    Error code: 0x70021
    Tag: 0xA5695862AAF8E63A
Failed to start creating the volume snapshot.

    Error code: 0x10C442
    Tag: 0x14181C22EF45B04E
The device is not ready

    Error code: 0xFFF0
    code = 2,147,942,421 (0x80070015)
    Tag: 0xBD28FDBD64EDB8BC
--------------------
Error code: 33
Module: 7
LineInfo: a5695862aaf8e63a
Fields:
Message: Unable to create volume snapshot
--------------------
Error code: 50242
Module: 16
LineInfo: 14181c22ef45b04e
Fields:
Message: Failed to start creating the volume snapshot.
--------------------
Error code: 65520
Module: 0
LineInfo: bd28fdbd64edb8bc
Fields:  code : 2147942421
Message: The device is not ready
--------------------
Task 'Incremental backup' has failed on machine 'ROY01.bbmd.local'.