This dialog displays when you try to edit a style sheet that is attached to topics which have not been converted to the latest format. You may have topics in your project that have not been converted yet if you opened the project and decided not to convert at that time, or if you imported topics into your project.
If you want to edit the style sheet, click OK and convert your topics. This may take several minutes if a large number of topics need to be converted.
Note: You may want to make a backup copy of your topics before you convert them.