I take it you are trying to use the playback through the web browser? If so have you tried a different browser? If its working on another computer it would suggest its not a firmware issue.. Try using IE if you are not already, and if thats not working I would suggest clearing your cache and resetting IE to default. When you install the plug-in make sure the browser is closed.
Also have you tried using the IVMS 4200 Software? its a much better way to control your devices that the web interface and version v2.03.00.05 is really nice.
