FPS Webplayer problem

I have developed a simple multi-user app consisting of two scenes- a login screen to access a server (running SmartFoxServer) and the main "room" scene in which people move around - the plan is to use it to view building models. The main room has a chat facility.

As a stand alone app it works - I (and others) can log onto the server and move around in the environment.

When I build the app as a Web player app I can log onto the server over a LAN test network but immediately after the main scene is loaded IE9 freezes, reports an error and shuts down. Same thing happens when I tested it with Firefox

If I build the app without the login scene to run locally on the build PC then it works in IE9.

Anyone have any ideas why this might be happening? I'm new to Unity so my knowledge/expereince is somewhat limited. Would appreciate any assistance.