Co-Op/ Multiplayer crash after few minutes - Heeeelp

[Mest]

I want to play Co-Op with my mates, but after a few minutes some of them stand still in my game at their pos, but actually they fight by my side...
and some minutes later the game Crashes...

Sinlgeplayer works fine,
cant set on "fullscreen" (its "windowed"),
i deleted my "out"-folder in the "documents" (didnt helped),
i reinstalled,
my graphic-card is on the newest standard,
im not using w-lan,
"-nologos" also tried

Hope Someone can help -.-

[frankchenella]

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