Undefined value found

Hello,

I ran across this problem in the computation, using Solid Mechanics and Fluid Flow.

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
.There are 553 equations giving NaN/Inf in the matrix rows for the variable mod1.u
. at coordinates: (-1.476e-005,-1.18654e-005), (-1.476e-005,-1.09231e-005), (-1.476e-005,-9.98073e-006), (-1.476e-005,-1.375e-005), (-1.476e-005,-1.28077e-005), ...
There are 553 equations giving NaN/Inf in the matrix rows for the variable mod1.v
. at coordinates: (-1.476e-005,-1.18654e-005), (-1.476e-005,-1.09231e-005), (-1.476e-005,-9.98073e-006), (-1.476e-005,-1.375e-005), (-1.476e-005,-1.28077e-005), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.

I tried to fine the mesh, but still got the problem. I tried to right-click Dependent Variables 1, compute to selected. It seems that there is nothing in the Stress (Solid), Surface 1, Deformation.

Would you please help to check this? Thanks a lot!