When i play counter-strike source on my pc, i get this message before the game even loads a level:
Internal driver error in IDerect3DDevice9::Present()

sometimes i can play a few levels then it comes up, sometimes it won't even load, sometimes there is no problem.

What does this mean??i assume it means that there is no 3d device, but all my other games work (including counter-strike condition zero) am i overloading my graphics card?? how can i fix it???