I am trying to model a solid with large deformation using user-defined constitutive model. The model failed in data check with error:

"Bad material definition in element number xxx instance xxx: zero or negative initial dilatational modulus caused by bad material data. Please check your material input and any initial conditions if necessary".

I understand that this error message indicates that there is something wrong with the VUMAT subroutine. However, using the exact same subroutine, I was able to run with CEL. So I guess there might be some difference in using VUMAT for CEL or SPH. Anyone could help me with that?

It may also worth mentioning that I firstly done the meshing with C3DBR and then using "conversion to particle" at 0 second to generate SPH particles. The error didn't say anything about my N C3DBR elements (where N is the total number of C3DBR elements), the error was only on the elements from Nth to 2N-th, which was not what I generated initially but generated following the "conversion to particle" commend.