Hey everyone! Tekkit is broken again!
Really easy fix. Search %appdata% on your computer and find a folder called Roaming. In this there should be a .techniclauncher or something along the lines. In there, you will find a folder named tekkit. Delete this.
(WARNING! YOU WILL LOSE YOUR WORLDS! As far as I know, it seems like your worlds are somewhat corrupted so this is unavoidable. If anyone knows better than this please post so I don't ruin this guy's day)
Once you have done that, run the Technic launcher and select tekkit. Log in and it should re-install everything. DO NOT UPDATE THE MODS! Ignore these messages. They are not for 1.2.5.