use of CINT command for J integral calculation of 3d model with ansys

I used for the first time the CINT command with ansys, and I get strange results:

negative values

very different values for 2 adjacent nodes on the crack front

non converging values (values fluctuating from 1 contour to another, going up and down)

Also, i don't know what are the units of the J integral (I am using SI units, dimensions in mm ).  It's important to know so I can calculate the SIF

How can I know what contour gives the best result? what are the units of the Jintegral in the SI.

Anybody have some information for me?

Thanks