Window Mode Problem

Whenever I go to the window mode (alt-enter), I get an error that says "This adapter cannot render 3D graphics in this windowed mode. Changing desktop settings may enable it to do so." I click ok and it goes to window mode but when I try to go back to full screen, I get just a large black square which is as far as it goes. I have to close and restart FS9. I don't have this problem in FS2002 which is still installed on my system. I'm using a GeForce4 Ti 4200 with 1024X768X32 resolution. Don't know what to change to fix this. Any ideas.Jim