Sorry about the issue. It means there's a character in your data that the app can't display correctly currently. This sometimes occurs if text contains 'smart' or 'curly' quotes (apostrohope, single quote, double quote, etc) instead of 'straight' quotes. Those curly quotes are often found in text that originated in Microsoft Office apps. In your text you should be able to just selected the bad character, delete it, and replace with with a normal or straight character.
