Warning message in Feflow 6.0

Hallo!
I'm using Feflow 6.
When I try to run the model, a warning message occurs:
[i]WARNING: Math: Argument domain error in function sqrt!
WARNING: BiCGSTABP matrix solution in 500 steps
(> 500 maximum iterations)
with errors: res_n = -1.#IND00e+00, res_ini = 1.#INF00e+00
WARNING: Math:  last message repeated 500 times.
WARNING: Math: Argument domain error in function pow!
WARNING: Math: Argument domain error in function sqrt!
WARNING: Math:  last message repeated 935887 times.
...
[/i]

I will appreciate any tip.

Best Regards

Matteo

For some reason, the model is highly instable: The solver reports a remaining error that is infinitely high after 500 iterations. I recommend to check the initial conditions, and - if they are OK - to try to find out what other reasons may be in the model causing the values to go through the roof.