Not to be a smart a**, but have you installed the DLC recently? I had the same issue when I did, & all I had to do was click Live & sign in. After signing in, close the game & find you saved games folder. There should be a new folder bearing the title of your gamer tag. Move the saved game files from your previous game into the one bearing your gamer tag name (only the files within the folder just so we are clear) Now go back into Fallout, click Live, and you should once again have access to your saved games.