It's very unlikely that this is caused by the gamepad alone. Perhaps it's because you have two game controllers plugged in instead of 1, or 1 instead of 0. Are you sure nothing else is different between the case when the error occurs and when it doesn't? It seems that it's happening during the Save operation because something caused it to try to save the main window into the saved game file. But it's not supposed to save the main window. Something must have unexpectedly established a link from a saved object to the game window. Do you have some customized code in your project that links a sprite or a player or something to the main window? (Maybe only when there is more than one controller plugged in?) Maybe it only happens if you visit the player options dialog when running the game? There must be some other difference. You could try to narrow the problem down by including only specific kinds of information in your save unit with IncludeInSaveUnit, then see which one causes the error.
