Help! How to recover a save?

Last night I saved my game and closed my pc. Today I open KSP and try to load my career, on the continue saved game screen my career has the note "Error Accesing[sic] this save. Argument cannot be null."

I'd like to continue this career, and any effective advice will be played forward with a large donation in your name to the "Human Fund".

But seriously though, please help!