Mesh Problem?

Hi, guys.

I got some problem with this message after computation.

'Failed to find a solution.
Singular matrix.

For mesh-case 0 there are 1 void equations (empty rows in matrix) for the variable mod1.mef.mi1.term1.V0_ode.
at coordinates: (0,0,0), ...
and similarly for the degrees of freedom (empty columns in matrix).
Returned solution is not converged.'

I think it is mesh problem but I do not know how to fix it.

I need your guys help!!!!

P.S I cannot attach my file because it is too large. Sorry.