Sorry if this is posted in the wrong place.

Has anyone else ran into this error?  It came up for me when I downloaded the game, to play multiplayer, onto my friend's computer (per the user agreement which states that you can make one additionally copy to play a networked multiplayer game)  and when either of us tried to join the other's game we got the above message:  "You don't have the files needed for this game."  we have the same version installed and are using one of the maps that came with the game so we both have the map we're trying to play (in this case Balance of power).

Any help or suggestions?