I had this problem yesterday.
I believe it is the maemo-launcher update that causes the problem, mainly because it cannot upgrade properly (as the table reboots when it senses maemo-launcher not running).

flash your 770 like so:
$./flasher-2.0 --set-rd-flags=no-lifeguard-reset

That will keep the 770 from rebooting when something critical has crashed or has been shut down for an upgrade.
You can then use --clear-rd-flags=no-lifeguard-reset to put it back to normal, but I havent at this time.