Nov 24 18:28:20 Tower kernel: sd 1:0:4:0: Power-on or device reset occurred
That's the start of everything. Disconnected itself.
Reboot is the only recourse. You can try a different USB port if problems continue, or alternatively install the Flash Remount plugin. (Not 100% sure if the plugin would have helped here as from that logged line onwards it's a wall of text and hard to see if the flash "reconnected" itself)
Honestly, out of all the diagnostics I look at, yours seems to be sending the most amount of emails of the bunch on a twice daily basis.