Nofollow links for all articles in 1 category

Hi !
I have a little problem on my website. I just to see that all my links of my articles in a specific category (the problem doesn’t happen for the others categories) are on nofollow. I really don’t understand why. Could you help me ?
The category is : http://www.pickupalliance.com/aborder-une-fille/ and an article in this category for example : http://www.pickupalliance.com/aborder-une-fille/comment-aborder-une-fille-en-groupe/
PS : I have the plugin Yoast
PS2 : in the back office I don’t see the nofollow attribute
Thank you