Solo. Although I did get an error on loading a game, stating that the server could not be started. I'm assuming this is because I'm currently running an Open Transport Tycoon Deluxe server on the port AI War usually uses. I'll see if restarting AI: War helps (I've changed ports on the server now).
Okay, I know what the problem is, then. Basically, the error you are getting from the Lidgren library means that some sort of non-Lidgren data was sent to the port that is in use by AI War, and Lidgren didn't know what to do with it.
Even if you've shut down the Lidgren server, if some other computer might be sending packets to that port still, then that could cause major issues. If you switch the AI War port to something else you've never used, I imagine that would make the problem go away.
One of the limitations of the network library that we use at the moment is that it's really not able to react well to extra data being sent its way. There is a newer version of the network library, but it's largely still in beta and last time I tried it it was crashing constantly with AI War, so I never did even a beta with that in it. I should try that again sometime soon, though.
For now, the main thing is to make sure that there aren't other programs sending other data to your AI War port, otherwise you'll get an error like you did here.
Perhaps that's not the issue, but my best guess is that it would be.
