Testimonial Category Page returning Soft 404

I created a few testimonials in highend theme, and a couple of testimonial categories.
They both return soft 404 (no results) even though there are 2/3 testimonials assigned to each of these categories.
e.g. http://socialvignerons.com/testimonial_category/fans/

I would assume these pages should return the testimonials assigned to the category rather than nothing !?!

Thanks for your help