Hey everyone, I'm new here. Ran into this problem and pulled my hair out until I found this forum. Thanks for the good ideas.
I run ubuntu Feisty and may have found a way for the more terminal-shy folks to deal with this in gui.
I also have the latest update of OS2008 on my N810. If you haven't updated yet, do it. This is a nice update with speed and stability tweaks plus a few really nice gui upgrades. Anyway, on to my fix.
As mentioned in an earlier post:
1) Shutdown the N810
2) Plug in to your usb port and reboot the N810
3) On your desktop, open "disk"
4) Highlight and delete pressing the delete button on your keyboard deleting all the contents (Yes, this will wipe everything, but you knew to back-up first, didn't you?)
5) You'll get the "Read Only" warning, simply cancel it.
6) Unmount both disks and disconnect the usb cable.
7) go into the File Manager on the N810 and select the Internal Disk. Click on Tools and Format the card.
This worked like a charm for me, I hope it helps someone here. Any feedback would be interesting. Good Luck!