Dear Lizet,
From what you describe, I would guess that your model is going numerically unstable because of too large of a time step. The smaller and stiffer the turbine, the smaller the time step requirement is. I would try a time step of 0.0001 s or 0.00001 s to see if you can get the model to run. Obviously, you want to choose as large of time step as possible while keeping the solution numerically stable. My rule of thumb for selecting the time step for the structural module is given in the following forum topic: FAST Integrator, step size & precision - #3 by Jason.Jonkman.
Best regards,