i had the same problem... here wht i did....


~ $ root


BusyBox v1.10.2 (Debian 3:1.10.2.legal-1osso30+0m5) built-in shell (ash)
Enter 'help' for a list of built-in commands.

Nokia-N900:~# mkfs.vfat -n MyDocs /dev/mmcblk0p1
mkfs.vfat 2.11 (12 Mar 2005)
Nokia-N900:~#

then enter

sudo gainroot
umount /dev/mmcblk0p1
fsck -af /dev/mmcblk0p1
mount /dev/mmcblk0p1 /home/user/MyDocs

than this came up
Nokia-N900:~# sudo gainroot
root is not in the sudoers file. This incident will be reported.
Nokia-N900:~# umount /dev/mmcblk0p1
umount: cannot umount /dev/mmcblk0p1: Invalid argument
Nokia-N900:~# fsck -af /dev/mmcblk0p1
fsck 1.41.3.maemo0 (12-Oct-2008)
dosfsck 2.11, 12 Mar 2005, FAT32, LFN
/dev/mmcblk0p1: 1 files, 1/1768863 clusters
Nokia-N900:~# mount /dev/mmcblk0p1 /home/user/MyDocs

checked my file manager and it was there.. the device memory. pressed on it and it saw the folders but they were empty.

checked memory from the setting and still it says memory corrupted, than went bk to the file manager and formated the Nokia N900, than checked again on the setting and finally it was back.

http://talk.maemo.org/showthread.php?t=71702&page=2