Invalid Steam ID Ticket/zh-hans
From Obsidian Conflict Wiki
如果你在游戏中被无缘无故的踢出因为"断开连接: 无效的STEAM用户" 关掉Steam, 打开你的STEAM目录, 删除文件"ClientRegistry.blob" 并且重新运行STEAM.
2011年11月25号更新: Recently we are getting a lot of reports of people unable to join Sourcemods (including OC) due to that error even after deleting the .blob file, if that's the case for you, do the following:
Shut down Steam, head to your Steam folder and delete everything except:
Steam.exe
"Steamapps" Folder (which contains your games so you won't have to download them again.)
[Optional to delete] "Userdata" folder (which contains your screenshots.)
And start up Steam again.