Elastic beam section in Example 5 (3D model)

[Rocky]

Dear all:

In the example 5, when I change the elastic section of all girders to fiber section involving nonlinearity, error occurs. The given hints are:
"WARNING - ForceBeamColumn3d::update - failed to get compatible element forces & deformations for element: [ele no.](dW: << -1.#IND, dW0: 2.52822e+56)"!
Would somebody be kind enough to tell me the reason why this happens for nonlinear formulation but not for elastic section?

Thanks in advance.

Rocky