There's not enough information to go by, really, and I certainly never had the problem, but you can try debugging it further yourself. Twine (on Windows at least) runs inside a browser - Chrome for me. After opening the tool, open the developer tools (F12) and there the console tab. Continue trying to import whatever story creates the problem and see what appears in the console. With some luck, you might be able to find out the source, or at least have enough information for others to debug the problem.