Alright, I think I found the problem! It worked after I encrypted my connection for testing purposes. So the problem must be network related in some way, probably located at my ISP. They block P2P traffic and use a web reputation filter that filters http, that might be a possible cause. The only question that remains: is there a way to permanently fix this for all users? I know I am not the only one with this problem and not everyone has access to a VPN to circumvent this. Since this seems to happen during the FML setup, maybe try contacting the forge team to provide an alternate method of acquiring the files? However: thanks to everyone for their effort. This was a rather exotic problem after all (although it could become a bigger deal in the future with more and more ISPs regulating traffic). Also: since I can't edit the thread title, can a mod change it so we know it is solved now?