@c4rl05,

How did you format the partition under Ubuntu? Hopefully as VFAT (FAT32).

If you for some reason formatted it as ext2/3/4 then you know the reason for your problems. Namely the files are most probably owned by your Ubuntu userid, not by N900 anymore.

Please run, as root on your N900: sfdisk -l (<- that's a lowercase L).
and post the results here.