Port access blocked from IIS site but not from direct connect

HI,

I have a site running IIS and dotnetnuke. I also have a socket server running on the same PC at port 4747.
A test app and a flash app can connect to the socket server if they are run direct from explorer or dragged into an IE window either locally of from a remote PC.
However if run from the iis site, either via DNN or pointed at the flash's URL directly they cannot access the socket server.
It cannot be a firewall thing as they can access it direct from the desktop etc.

Does anyone have any ideas on what might be blocking it when accessed from IIS sites.

Thanks in advance

Mike Fox