Problems with dhmlxWindow object in explorer 8

im working with the dhtmlxWindow object my problems it when i open a window in firefox works fine but when i open the same window in internet explorer 8 i have this warning ‘Invalid argument’ at Line: 1343 Char: 24 Code: 0 URI: localhost/cmaster/codebase/dhtmlx.js what it wrong? i copy the code exactly as the demo code

could you send the completed demo ?