So, first I only removed the 2 added files and renamed my Assembly-CSharp.dll.OLD back to normal. Restarted the server, nothing, nada, server running, but no connection possible. output_log.txt shhows exactly the same rrors as posted above. So I replaced the whole 7daystodie_data/managed forlder with the one from my local backup, restarted the server and voila, I can connect. Seems some file in the managed folder gets changed/corrupted during starting with the modified files. Since the logfile is too long to post here, I've uploaded it here logfile.txt