Could not connect to the network!

[svpforever]

Can anyone solve this problem for my friend please, we're trying to play Warcraft on version 1.26a. After the installation, he (using Mac, me PC) can normally start game but can't access Local Area Network and it said "Could not connect to the network".... and why don't we play newest version of warcraft, it kinda complicated and i don't good at English much to explain so please help