-Fun box has been haveing some issues with Dropping players as of lately. When a custom map is loaded it generally kicks people.
-also in addition to that if he has a incrediby high ping this may also cause a disconnection from server i would check to see if it could be over 300 ping
-Has he tried to play on other servers by any chance to make sure that its not limited to Funbox?
the host file fix you mention may be causing some issues i would revert the changes he has made and try the one in this post to see if it give's him any improvements "couldnt hurt to try"https://docs.google.com/document/d/15018Lo99LlyyV2MgzUQN6rUPnWXCXN27oNr0Jh5JAx8/edit?pli=1#heading=h.3dy6vkm
-he can also try and see if Not using the Autoexct you mentioned by renaming it before launching MWLL to see if this could be a factor for his disconnects.
-Lastly he can try clearing his Shader cache this has been known to cause funny odd glitches for many reasons