Syslog might show why it thinks it needs to reboot. If you don't have it installed you may be able to install it by booting the working version, chrooting into the reboot-looping one and installing it manually with apt-get (see http://maemo.org/development/tools/diablo/ for installation details). While you're in the chroot you may want to try uninstalling autoscan to see if it makes a difference.

See also http://wiki.maemo.org/Troubleshooting_boot_issues