I also have a NVIDIA 6800. Maybe the problem is related to this card?
I'm having to play EP3 on my Notebook as I could not play it on my machine yet. The splash screen opens up and, when I hi PLAY, the game exits with that error message. I've made 6 tries in a row and left the errors on screen on the following image, in order to better show the different messages:
The computer specs are:
Brazilian Portuguese Windows XP SP2
NVidia 6800 128MB - Latest NVidia Drivers (just downloaded)
Pentium 4 3GHz
Please note that EP1, EP2, CSI Demo, Bones 1 and Bones 2 run perfectly on this computer. Just tried them all. This is specific to EP3. Also tried deleting the props file - no luck.
I hope this helps finding the error.