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!
I just had a similar issue, Turns out the \bin\ and \gamedata\ folders and fa_path.lua in C:/ProgramData\FAForever were placed into C:\ProgramData\FAForever\replaydata instead. Maybe because the first thing I did (after locating the game folder) was try to watch a replay? Moving those (back?) fixed it.