I have never fired a kerbal and have never lost one yet I still get this lock up occasionally. I have never added any 'Mods' either. Most of the time it happens when I start the game but has sometimes happened in the VAB, which leaves a forced close as the only way out. I find it strange that any ship I build and save is available later. On starting the game I visit 'Mission Control' before trying anything else. Frequently I find that it shows 99 contracts with Max=0. When this happens I hit the exit arrow in the upper right corner, then the game date/time appears at the bottom of the screen but I am still in 'Mission Control' and can't leave. When this happens I hit the Escape key and it brings up the 'normal' pop-up menu but the only thing I can do is load a previously saved game. Therefore, I have been creating a 'Save' game before exiting the game. When I load this saved game everything goes to a normal screen and when I check 'Mission Control' it shows the correct number of contracts and game play is normal until the next lock up