Use the marquee tool to select half the building on plan. Press F5 to open this the selected area in the 3d window. If the error message stops, you know that the door with the error is in the other half. Keep repeating using smaller areas to narrow it down.
You will probably find you have entered an impossible dimension into the door showing the problem. Try looking at the frame parameters first. Correct this and the error should stop.
If all else fails, delete and place a new one!
Hope that helps!
