Windows Media Player Error

[ShadowPuppet]

Hello.
So I just received the season 1 box set of Ghost Whisperer in the mail yesterday. I watched two episodes on Windows Media Player on my Windows 7 Acer lappy. Everything worked fine.

Tonight I tried to watch one of the disks again; I never touched the program since last night although it's been open. I however am now getting this message:
"Windows Media Player cannot play this DVD because there is a problem with digital copy protection between your DVD drive, decoder, and video card. Try installing an updated driver for your video card."

As previously stated, it worked fine last night and has for the year I have had this lappy. I never did anything to alter the program or it's settings thus possibly confusing it or doing something wrong.
I don't understand why I am having this problem now and I while I am decent with computers I do not know anything about video cards.
What is this message indicating? What must I do?