There's a bug in fvwm95-2.0.43a, which causes the window manager to crash when one tries to iconize a window for wich no icon-name was registered. The patch enclosed in fvwm95-2.0.43a.patch fixes the problem. To apply it, cd to the fvwm95-2.0.43a-Whatever/fvwm directory, then enter the command: patch < fvwm95-2.0.43a.patch