s1st, 515t..whatever..

What does this mean?  I would get this on my box more often than not after a reboot and to clear it I would need to reboot again.  I finally had enough issues with the old box that I had it replaced and now this morning I get the display again.  I saw only one former post where this particular error was mentioned and there was no answers, just a 'let me know if you see it again'.