Made my first 2 coasters today :( anyone else ever had this happen?

I was burning a dvd, Liteon 851@ 832 using nero 6, I've burned maybe 100 or so dvd's with 0 problems.
Today I goto write a movie, and I get one coaster, try it again, and get a 2nd!!

The problem was this:
nero started writing the dvd, got about 39%, then the main buffer emptied out to zero, at which point the light on my dvdr went from orange to yellow, the disc kept spinning, the buffer refilled, but it never started burning again. I left it for 12 mins after it got stuck at 39% and the buffer refilled, and it just sat there spinning.. The drive was locked out, couldnt shut nero down with ctrl-alt-del, couldnt eject the disc, and couldnt do anything to stop the drive from spinning other than resetting the machine.

I've never ever had this happen and was wondering why it would do this now all of the sudden. I'm running xp pro with 512 ddr, I have nothing running in the background but a firewall and a temperature probe..
anyone have any idea what in the hell caused the buffer to empty and stop the disc from writing, but keep it spinning?
thanks

Try Defragging Your Hd. It Could Be Something That Simple To Make A Coaster.