It may be a client side glitch, I've never got this before. What software do you run the game on? Er, rather, do you have it downloaded or are you on web. If your on web you may have to just wipe the cookies on the page and reload. If it's downloaded I'd try deleting the game and retrying. And yes I know It's frustrating to lose all the work you put in... But if you have it downloaded you could easily copy the save file or files into another folder elsewhere, re-download the game and just replace the files. Idk if ANY of this will help but It's here...