Ok, still no luck. I went and started a whole new app with just the basic DirectX initialisation and tried to copy a portion of one surface to another using that code, but it drops out. I wonder if it has anything to do with BltFast? I'm at a loss here. Any ideas? It can't be in my coding, because if I just load a graphic directly into the main surface from disk, it works fine. Only when trying to load a portion of one surface into the main surface do I have a problem. the dimensions are correct, too.