My friend and I have the same problem. He has Trinity, and I bought them individually. We're both playing Diplomacy v1.34, but it keeps saying our mesh files are different and one of us has a different version, which we don't. We've been playing together on this for years, but this problem keeps cropping up every time we've tried to play since the last update. Really frustrating...
P.S. Also, we both recently reinstalled everything, and the problem keeps happening...