I added Project red after I created the world. The world saving problem is something I've run into before after I've lost a world and then got it back.Just a question ... can you create a new world without Project Red in it, then after loading it, log out and add all of the Project Red mods that are in the other FTB packs? From what I can understand in the error log, its calling a method that doesnt exist. Try using the most recent versions of Project Red for 1.6.4 from Project Red's Website and follow the install instructions on the page.
If the problem persists with the most recent version, check their bug tracker to see if anyone else has the same problem. If no-one does, submit a new issue there.