Question about calculating K factors at a bimaterial interface crack using ABAQUS

I am trying to calculate J-integral and K factors at a bimaterial interface crack using ABAQUS, but not very successful. The bimaterial consists of a layer with orthotropic material property and the other with isotropic material property. The crack lies at the interface between those two materials and only can grow along the interface. I used rectangular elements for the whole structure, including the crack tip region. I used "*contour integral" keyword to specify the quantity type, i.e. J-integral or K factors, to calculate. It seems the code run through without a problem for J-integral but give me error messages for K-factors. The error is "material along the crackfonrt must be of the same type for the calculation of K factors". How to solve this issue? Does this "same type" mean must be both isotropic material? If so, how to calculate those quantites for orthotropic/isotropic bimaterial interface using ABAQUS? Any suggestions are more than welcome. Thanks.

XW