The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
Menu->Settings>Forged Alliance Forever
[Game Location]
Make sure you game location is specified and correct, the error looks like it can't locate the exe file for the game. Either that, or it has a permission issue accessing the game. (try right-click run as admin and see if that fixes also)