You shouldn't need to restart the save. I was able to access it again even though I had it unlocked on my save. Did the dialog change each time you failed? Did you get the "Integer overflow" error?
Sounds like a bug to me. You could try reinstalling the game, or using a different save file. What OS are you using? Obviously I can only help so much, as I did not make the game. But it always helps developers to know exactly what's going on.
