First of all: If you still play Doom 3 at all, you should be using the "Dhewm 3" version, which doesn't change the game at all except updating some of the under-the-hood stuff so that it works with widescreen and modern surround sound setups and such. https://github.com/dhewm/dhewm3/releases

On to the problem: While Dhewm 3 is a replacement .exe and so should be able to load mods like the original .exe rather than being a mod itself, it still doesn't seem to play nice with/load without crashing Last Man Standing, the only Doom 3 coop-enabling mod that's stood the test of time. http://www.moddb.com/mods/last-man-standing-coop/downloads

Can anyone get these to work? Does anyone have any ideas? Any help would be appreciated. I tried googling all the error messages that popped up, but they were standard ones that people would get starting regular Doom 3, and seemed to mostly relate to verifying your key, but I did all the stuff the internet recommended and it didn't help.

Thanks in advance!