Cant play Portal 2 with friend (help)

[Space Man]

I am trying to play Portal 2 with a friend, but every time I attempt to play it simply says that my partner disconnected. I accepted an invite from my friend , after I invited him first, but received the same error. I have browsed the steam support page, but found nothing in relationship with my error and portal 2. I have validated my game cache with 1 file in question. I re validated again and found that one file was still missing . I do not have an issue connected with friends in any other online play and do not know what the issue could be other than this one missing file.

[YuMS]

Same~

[Space Man]

After looking around on the web I have found that a lot of people have this issue, yet when they resolve it, they never say how they did so...

[BurningSkyZ]

Is your and his/her Web okay? or do you downloading anithing while its Connecting?

[DXGames]

I suppose you may also have such problem due to your firewall software. Try to shut it down before the next time you gonna play. If it helps then just add the game to your firewall exception list.