Backup user files to PC server

[bill from maine]

Hi,

I'm trying to backup user files to a disk image that I am directing to a PC server.
I can write to the PC server fine.
I can do the above function fine to the Mac hard drive.
However, when I try to backup the user files to the disk image on the PC server, SD tells me that it failed to mount the disk.

Heres the log:
| 01:47:01 PM | Info | SuperDuper!, 2.5 (84), path: /Applications/SuperDuper!.app, Mac OS 10.5.4 build 9E25 (ppc)
| 01:47:01 PM | Info | Started on Thu, Jan 29, 2009 at 1:47 PM
| 01:47:01 PM | Info | Source Volume: Macintosh HD, mount: /, device: /dev/disk0s3, media: Maxtor 6Y080M0 Maxtor 6Y080M0, interconnect: Internal ATA, file system: "Journaled HFS+", OS: 10.5.4 (9E25), capacity: 76.21 GB, used: 36.63 GB, directories: 164296, files: 711049, ejectable: NO, ACLs: Enabled
| 01:47:01 PM | Info | Target Image: /Volumes/Public/Marketing/Mac Backup/test.sparseimage, name: test
| 01:47:01 PM | Info | Copy Mode : Smart Update
| 01:47:01 PM | Info | Copy Script : Backup - user files.dset
| 01:47:01 PM | Info | Transcript : BuildTranscript.plist
| 01:47:02 PM | Info | PHASE: 1. Prepare to Copy Files
| 01:47:02 PM | Info | ...ACTION: Preparing Macintosh HD
| 01:47:02 PM | Info | ......COMMAND => Verifying the integrity of volinfo.database
| 01:47:03 PM | Info | volinfo.database OK
| 01:47:03 PM | Info | ......COMMAND => Enabling permissions on Macintosh HD
| 01:47:03 PM | Info | Refreshing Disk Arbitration ...
| 01:47:04 PM | Info | ......COMMAND => Verifying that permissions are enabled for Macintosh HD
| 01:47:04 PM | Info | Permissions on '/' are enabled.
| 01:47:04 PM | Info | ...ACTION: Mounting test
| 01:47:04 PM | Info | ......COMMAND => Preparing test
| 01:47:07 PM | Info | hdiutil: create failed - Permission denied
| 01:47:07 PM | Error | ****FAILED****: result=256 errno=0 (Unknown error: 0)