abaqus vumat-excessive distortion

Hi All

I am trying to implement a composite material model in vumat. So far, I
have been successful in getting the correct results for a cube for both
tension and compression with the cube being modeled with just one
element (C3D8R)

But when, i model the same cube (side 40mm) with 125 elements,
subjected to the same bc's, with the same material parameters, i get an
error that the element is undergoing excessive distortion.

I am specifying a density of 1.52e-9 ton/mm3.

What could be the reason for this error ? How do i go about this ?
Since I will also be using the same subroutine for carrying out impact
analysis,could anyone please suggest any additional care that i need to
take for that ?

Thank You