First what is the model of your player? Sony has alot of know issues with Blu-Ray as well as alot of others. HD-DVD seems to be a bit better with not having these problems apparently.
First, make sure your monitor is running at it's native resolution. If that doesn't work, try every other resolution and play the video. Sometimes monitors will only run HDCP compliance in certain video sizes... Don't know why. :-\
Also, what DVD program are you using? Some earlier programs have problems with HDCP Compliance. Make sure you have the most recent update of your DVD Player software. If you don't, un-install it and get the most recent version and re-install it. Don't just patch it!
The video card is definantly complaint as well as monitor. Double check you are using a DVI cable though, not VGA.
Also, running two monitors will work so make sure you are using only one, and that the second one is definantly disabled.
If you still can't get it to work there is software that will ultimately bypass it so you won't get that crap. Here is the link:
SlySoft AnyDVD HD
Hope something I said helps.