DVD Player stops reading DVD

Hello,
I put a "Family Guy" DVD in my Denon player early today. The player could read and play the DVD without any problem. The Denon is about three or four years old and was top-of-the-line when I purchased it (able to play super audio CDs, etc). The Family Guy DVD stayed in the player all day long spinning. When I cam home the Denon had shut itself off and when I turned it back on it could not read the DVD. I put the DVD into my computers (I have a Mac and a Windows XP) and they could read it fine. The Family Guy DVD is one disk of a series. I put the next one of the series into the Denon and it could read it.

What happened? Did leaving the DVD in the player for so long somehow corrupt the DVD player's ability to read the DVD?

Any help or advise here would be appreciated.

Thanks, Mike Rees