Ubuntu :: Unison Sync To Fat32 Permissions?

My system consists of a laptop running Ubuntu 9.10, a network drive (Samba share formatted fat32 the only option) and a desktop PC running Windows XP. For several weeks have been trying to set-up Unison to synchronise files between my laptop and a network drive with only limited success. I mount the network drive locally with:

sudo mount -t cifs //netdrive/store /home/gm/NAS -o guest,rw,iocharset=utf8,file_mode=0777,dir_mode=07 77.

Then in Unison (graphical interface),

root 1 is: /home/gm/Shared_Docs
root 2 is: /home/gm/NAS/HomeBackup/Shared_Docs_Backup

After clicking the �OK� button, Unison searches for changes files and I click �Go�.

An error is then produced, a sample of which would be:

�Error in renaming /home/gm/NAS/HomeBackup/Shared_Docs_Backup/.unison.Our-inv.xlsx.f3e8034159989f9de7081f9154319a2b.unison.t mp to /home/gm/NAS/HomeBackup/Shared_Docs_Backup/Our-inv.xlsx:
Input/output error [rename(/home/gm/NAS/HomeBackup/Shared_Docs_Backup/.unison.Our-inv.xlsx.f3e8034159989f9de7081f9154319a2b.unison.t mp)]�

If all files in the destination directory (root 2) are first deleted, all files are copied correctly without errors so, I think the problem may be caused by permissions where Unison is unable to overwrite the original file. I know formatting the network drive fat32 is probably making the matter worse, unfortunately I have no alternative.