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?

Not sure what changed, I haven't rebooted or anything but today I can user the card, must have just taken a while for the device to release it

I'm happy your problem resolved itself. If you run into a similar problem on a Linux system in the future, try the lsof terminal utility.

"lsof" stands for "list open files". Pipe (send) the output to grep to limit the listing to open files on the memory cards. The command "lsof | grep mmc" should tell you what programs have which files open on the memory cards.

The media-scanner crawler thingy was probably scanning your card, thus the reason for it being in use. Try rebooting then waiting about 1 minute. Usually works for me.

just open and close the memory card door.. i do it all the time. metalayer crawler literally crawls through my memory card because i have a lot of saved web pages and small files.