X Error: BadWindow in X.err

Hi Folks-- I've been meaning to ask about this but haven't got around to it til now. My X.err logfile contains dozens of instances of the same error: X Error: BadWindow (invalid Window parameter) 3 Major opcode: 20 Minor opcode: 0 Resource id: 0x2a00002 (or another number) ...As well as a few others but one thing at a time. As far as I can tell the error doesn't cause any harm, but it just bothers me. Is there anything I can do to fix it? Thanks.... :-)