If you have WMP11 final installed on your PC then you should downgrade it and it can be a problem.

You may use WMP11 beta instead of WMP10.

You should also disable Automatic Update of your Windows.

And don't forget to use the latest version of FU4WM (1.3 fix).

Also don't buy media content. Try test content from ezdrm.com and fairuse4wm.