Has anyone here ever used Arlequin before? - (Jul/29/2008 )

I met a problem when I was calculating the genetic distances between individuals based on certain molecular markers. Negative values (D<0) came out when I was using Kimura-2 parameter. I do not know whether it is because of the incorrect input data format or there is some special meaning of negative genetic distance values?
I need someone's help eagerly and I will strongly appreciate anyone who gives any comment or suggestion. Thank you.