Sync Error Thread

My friend and I are playing railroad. He only has a copy of soul storm and UA installed. I have all the games under my steam account and UA installed. We've played a few games together, him as Sisters and myself as Space Marine, but we've been unable to connect since due to sync errors. We've tried different armies on railroad, and different combinations. Both as inquisition, inquisition + tyranid, etc, but whenever the game loads we get the same sync error. Any thoughts? We're on the same iteration of UA as I used the same links he did to install.