The router reboot itself and it shows kernel panic, it could be possible corrupted package?
[7stones@Kamote] /log> print
jan/01/2002 09:00:02 system,error,critical System rebooted because of kernel failure
make sure you are running latest RouterOS and you still have this problem. Then create support output file and send it to support.
We had this on a couple af 800s with heat issues. It gets around 45deg c here and by adding more vent holes and fans we sorted this out.