Matrix has zero on diagonal

I have to solve a lid driven cavity (laminar flow) + melting problem (heat transfer in fluids and solids with moving mesh). I was able to successfully implement this in 2D.

I have now shifted to a 3D model, still solving the same physics. I get an distinct ( i haven't encountered this previously) error message which I’m unable to understand :
Failed to find a solution for the initial parameter.
Matrix has zero on diagonal for the SSOR update submatrix in the Vanka algorithm.
Returned solution is not converged.

In the Comsol reference manual, explanation for matrix equation for vanka algorithm is attached in the picture

Is the diagonal element (Sj) = 0? This S corresponds to the average values of the velocity vectors?
My initial condition is set to zero.

I have also attached my model file.

Kindly help