Backup problems

Hi!
I just got my phone back after getting installed the Norwegian language pack. I had made a backup just before I delivered at the store. When restoring it, after a while I got a message that the disk was full. I found this strange, but the storage manager in the control panel also told me so. I then chose to reset the phone, which apparently also erased the langue pack... Well, I tried restoring the backup file again, but again I was told that the disk was full, sometime when restoring my message file. Now how can I completely erase the disk in the phone, so that I can restore the backup I made_