Dear Holger,
This warning is unrelated to the FEFLOW power functions. Instead, it is a math (system) warning that refers to an exponential expression that evaluates to a value greater than the largest flaoting-point number that can be expressed (~10^308). With FEFLOW 5.3, parameter overflows are reported much earlier than before, but in most cases that's not critical.
Unless the consequences are obvious, it's hard to say where the error specifically originates.
I think, you can probably ignore that. It would be better to run the model with 'automativ time step control' in spite of warning as with constant time steps. Because that makes the simulation more instable, beside you have choosen really small time steps.
Regards
Kerstin
Regards