okay, thanks...

the issue was, actually, that on occasion it would simply -stop- downloading videos, complaining that my card had a read-only filesystem (and it had, in fact, somehow become read-only). Rebooting the N800 fixes it, until it happens again... to subvert the obvious response: no, I'm not removing/re-inserting or otherwise manipulating the SD card in any way when this occurs.

second question: there are other "youtube-dl like" scripts available for other video sites... is it possible/easy to configure myTube to allow these to work as well? ...or, can it be easily added to the myTube configuration somewhere?