Plutonium

Dss0 he's on that version but im on r3259, how do i update it?

So I have been trying to play black opps 1 zombie with friends recently. Whenever I join them while loading into the map I get an error and get booted. But when they join me, they spawn into the game with an ak_74u that is actually their m1911. But on top of all that they cant use their knife, and whatever gun they purchase turns into some other gun. Its super weird and I dont know if im explaining it very well but it makes the game unplayable for them. Also I've tried uninstalling the entire game and it didn't fix it, so I don't know what else to do.