LAN Data File Error

I recently spent several hours trying to get a LAN coop game working between two computers.  It kept giving that "game data files do not match" message with the red font, even though I was running swat on each computer from an identical install.  The crazy thing is I had it working before with this exact same setup but now it won't work even with those uninstall files moved out of the directory which had fixed it before. 

I'm not sure if this could be an issue with some sort of windows temp file or AV/firewall...

What was your choices for 2D menus on both machines?

For some reason "Use original Swat 3 menu - no custom menu" caused that error in multiplayer. I tried it out on the NeuWon network for the short period it was up and couldn't figure out what caused it.

I always meant to do more LAN testing for the whole mod but never got around to it. I figured it was lower priority since more people probably played it single player today.

I may have to move that priority up.

If I recall the GOG Install puts a unins000.dat in the folder? which causes issues, can't recall if the Last Resort installer took care of that in more recent versions or not.

Ya the installer still renames it to .bak if it finds it.
Good catch regardless.

TY for the assist SJ an DS, I had this issue the first time I tried LAN multiplayer with the two computers and was able to get past it by removing those GOG uninstall files.  I am running a vanilla version of S3 from identical folders containing the game install with swat.exe file associated files.  This worked last time I did it but now its not working.  One computer is running Windows 10 and the other is running Windows 7.  I have a nagging suspicion that there is a temp file lurking somewhere on the Windows 10 machine causing the error, another issue I am having is that if I have headphones plugged in when playing swat there is no sound in-game.  I am ok with dealing with a lot of random glitches and working around them but with this LAN data file mismatch error I have hit a complete brick wall and I am hesitant to spend much more time on it unless I have a clear idea of what is causing the issue.  In a way I think this would be a good general troubleshooting test case because getting to do LAN coop matches is a super fun aspect of the game that could keep the torch burning for that much longer if people are able to work past them.