O.K. How much free space do you have on the N800 itself?

By default Maemo Recorder records to the N800's MyDocs directory somewhere. I was recording my teacher in a class for a few hours when suddenly the recorder wouldn't record anymore. After I assigned it to record to my SD card, and moved the previous recordings from the N800 to the card, it started working again.

But you may have some other issue that hopefully can be resolved.