UDP Multicast Sockets

[Ophir]

Hello !

I have encountered something that I could not find an explanation for
it.

I have two applications both open an UDP Multicast Socket on port
1900(UPNP) without the system shouting that that address is in use.

When I try to open a Winsock on that address I immediately get the
Address in use error.

I can open many instances of those applications, and no error occure
and all of them work fine - Getting and transmitting Multicast
messages.

How is it possible? Is there some secret way of openning two or more
UDP sockets on the same IP Port???

Need help ASAP.

Thanks

Ophir.