After my quiting Fvwm-2.5, these messages were displayed on screen:
X Error of failed request: BadDrawable (invalid Pixmap or Window parameter)
Major opcode of failed request: 62 (X_CopyArea)
Resource id in failed request: 0xe0000c
Serial number of failed request: 265
Current serial number in output stream: 269
They were only displayed after quiting Fvwm2, not after quiting Gnome or Kde. I am not sure if it was Fvwm2's problem . Could you give me some advice on avoiding these messages?