I believe N810's had a problem with the internal memory being partitioned incorrectly from the factory, which leads to corruption. Search the forums.
Code: umount /media/mmc2 fsck.vfat -r /dev/mmcblk0p1 mount /dev/mmcblk0p1 /media/mmc2
umount /media/mmc2 fsck.vfat -r /dev/mmcblk0p1 mount /dev/mmcblk0p1 /media/mmc2