well i deleted all of my ftb beta stuff, and now it won't let me download the official release of ftb.com. it says it can't find the server.If you downloaded the 3.1 beta please wait for the release that will be out soon and re try.
My guess would be that you tried to add a new launcher into an old folder.
Put it into a new folder and run it again if you want to try this beta (no idea why)