Issue using bicgstab with ilu for preconditioning

I'm coding a 2D CVFEM solver using bicgstab with ilu to get preconditioners and I'm getting the following error:

??? Error using ==> ilu There is a pivot equal to zero. Consider decreasing the drop tolerance or consider using the 'udiag' option.

I use the udiag option and a different factorization options (crout, milu, etc) with same result.

What you think is the origin of my problem?

Thanks in advance.