I was try to copy some files (movies, comic books, etc) to the external 16 GB SDHC card on my N800 when the unit rebooted itself (I'm booting off an internal 8 GB SDHC) now, even after a reboot when I connect to a PC via USB it tells me both cards are in use and therefore I can't transfer files to it.

I've tried booting without the external card installed and then plugging it in after which doesn't help. Any ideas?