Warning about "Incomplete satisfaction of flow constraints..."

When I run a coupled flow and transport model, i always get a warning "Incomplete satisfaction of flow constraints within 30 iterative cycles at time=3.100000e+001 [d]. Termination of cycling."

I can't find any information from either mannual or reference. So what is the reason cause this warning and what will happen to the simulation results? Any one has experiences this problem?

Thanks

The warning refers to a free outflow on the top of the model. You have set the behavior of the model in case of head above the model top to 'constrained'. That means that all water exceeding the top is taken from the model via an (internal) Dirichlet boundary. That boundary has to be turned on in locations where the head exceeds the top only, which is done in an iterative way. If after 30 iterations the correct locations of the boundary conditions are not found, which is typically the case if the water level exceeds the top in large areas, the iteration is stopped and the last locations are used.

Is it possible to change the number of 30 iterations ? I am feeling like having half of that number will not affect the results, while it will decrease the running time.

Cheers
Didier

how to  turned boundary  on in locations where the head exceeds the top only?