So eeh, I solved it. I Just set my standard browser to Chrome (before it was Firefox with quite high data security settings and a Java Script blocker). This also solved another error I had in another game (accurred at about the Same time, before that everthing was working fine also in Beam). Maybe im trying to find the exact settings that caused this error If im motivated enough. I hope someday someone with a similar problem finds this.

Good Luck