The duplicate category dialog will appear when you are importing a category from another Resort Software database and that category already exists in the destination database. See the following image.
To keep the existing data in the destination database, click the "Keep existing" button and the category you are importing will be discarded.
To overwrite the existing category with the category you are importing, click the "Overwrite existing" button.
To cancel the entire import operation, click the "Cancel operation" button and you will be returned to the last opened form.