Problem streaming video multicast

[ambeer]

So on server i run vlc player, and run multicast over address 239.255.1.1:1234 for example, it runs fine, and on other computer i try to open network stream, add this address with port but everytime get error: Unable to open 'udp://@239.255.1.1'... why it could be?

when i try unicast it works grate! but i have no success to play video file using multicasting...

thanks for replies