We’ve been working for a few months recently on some OpenGL based PC game and I just discovered strange behaviour - only with GeForce 4 MX card.
The game works in fullscreen mode only. When pressed ALT + TAB under windows (XP) it suddenly outputs GL_INVALID_OPERATION.

Did anyone have similar problems?

Thanks in advance for any hints.

I don’t have similar problems, but you always can track down the function which causes the error using more checks in your code and then the discussion may be more informative.