A few comments :

1) Some N810:s have had a problem with corrupt memory solvable by the user.
I can't find the article in the wiki, but here is the original thread :
http://talk.maemo.org/showthread.php...corrupt+memory

2) I had (similar?) problems with my N810 memory cards after playing around with partitioning before I managed to do it properly with PB's console tools.
Formatting the cards from my PC plus reformatting from the PB program to the proper file systems solved the issue.
On this forum you can find several recommendations to use Memory Card Formatting Program from Panasonic on your PC.