"game version mismatch" bug making me and my friend unable to play with eachother

[Valentine_]

so basically yesterday me and my friend decided we wanted to play origins on bo2. so we got on like we normally do and I start up a lobby. he tries to join, then gets an infinite loading bug that just says loading fast file over and over. so we decide he should host, when I joined him the loading screen was a bunch of grey and blue squares and after it finished loading it kicked me out and says "game version mismatch" with some kind of error code I don't remember. we both tried reinstalling and basically everything we thought to do but it just wont fix. any kind of solutions

[Resxt]

Valentine_ solution is simple: is any of you using his Steam files? If yes then he didn't install the DLC and you obviously cannot play DLC maps without installing DLC so read the install guide.

Other case is if one of you is using files not from the install guide then delete that and get the files from the install guide instead

[Valentine_]

@lResxt both of us use files we got from a youtube video a few months ago, we dont use steam versions of the game

[Valentine_]

@lResxt i also just found out that in the bootstrapper (like the command prompt thingy) he gets a bunch of yellow text saying unknown command session_rejoinsession

[JezuzLizard]

Valentine_ That error doesn't do anything bad.

https://plutonium.pw/docs/repair/#how-to-repair-your-game-files