This most likely due to you having moved the KSP executable, (KSP.app for mac or KSP.exe for windows). You are not supposed to move anything out of the KSP root folder (KSP_win or KSP_osx folder). If you did move it, please try putting it back, then everything should work. Also, keep in mind that sometimes mods break the game causing it to fail to load. If this started happening after you installed mods to your game you may want to remove them. If none of the above is the problem contact us via Support Ticket to get another solution.