I'm just going to chuck all the fixes into this thread as I'm seeing so many of the same threads about the same solved errors.
Error 1 (I can't get the game to load I get the error with my jar file)
First of all download the game you have already have the required java's and winrar if you have these then you should extract all the files from the winrar popup onto a folder on your desktop. When you have done that run the game. If this does not work check this thread.