Oh shit! Well hopefully you were enjoying the game up until that happened lol. That is really weird, I don't think I've encountered that error before. If you take a screenshot of the error screen I can try to help you fix it, but like you said, it probably has something to do with the save data. If you go to your Appdata folder (C:/Users/[your name]/Appdata/Local), there should be a folder called Gun_Rounds, and if you delete savegame.sav from the folder and try restart the game, that might fix it. Fingers crossed!