Could be a corrupt persistent save file. Back your career folder up somewhere (your career should be there : Kerbal Space Program\saves\AUG 16) and try this:
delete persistent.sfs (it's the corrupt file)
duplicate the most recent quicksave #xxx.sfs and rename it persistent.sfs
try loading your game (you may need to restart the game)
if you load a craft in the tracking station and hit F9, you MAY be able to restore your progress (the one you have lost when deleting the corrupt persistent.sfs file).
if it doesn't work, try with an older quicksave #yyy.sfs file...
You'll obviously loose some progress but you'll play again.
SnakyLeVrai's post in Unable to open save file was marked as the answer