how can resolve this error in step-57,
Scanning dependencies of target step-57
[ 33%] Building CXX object CMakeFiles/step-57.dir/step-57.cc.o
[ 66%] Linking CXX executable step-57
[ 66%] Built target step-57
[100%] Run step-57 with Debug configuration
grid refinements: 0
viscosity: 0.1
Number of active cells: 432
Number of degrees of freedom: 4188 (3696 + 492)
FGMRES steps: 0
The residual of initial guess is 0
----------------------------------------------------
Exception on processing:
--------------------------------------------------------
An error occurred in line <534> of file </home/MATH/zeb/deal/dealii-9.1.1/source/grid/grid_tools_dof_handlers.cc> in function
std::pair<typename MeshType<dim, spacedim>::active_cell_iterator, dealii::Point<dim> > dealii::GridTools::{anonymous}::find_active_cell_around_point_tolerance(const dealii::Mapping<dim, spacedim>&, const MeshType<dim, spacedim>&, const dealii::Point<spacedim>&, const std::vector<bool>&, double) [with int dim = 2; MeshType = dealii::DoFHandler; int spacedim = 2; typename MeshType<dim, spacedim>::active_cell_iterator = dealii::TriaActiveIterator<dealii::DoFCellAccessor<dealii::DoFHandler<2, 2>, false> >]
The violated condition was:
best_cell.first.state() == IteratorState::valid
Additional information:
The point <0.5 0.42> could not be found inside any of the subcells of a coarse grid cell.
--------------------------------------------------------
Aborting!
----------------------------------------------------
CMakeFiles/run.dir/build.make:57: recipe for target 'CMakeFiles/run' failed
make[3]: *** [CMakeFiles/run] Error 1
CMakeFiles/Makefile2:195: recipe for target 'CMakeFiles/run.dir/all' failed
make[2]: *** [CMakeFiles/run.dir/all] Error 2
CMakeFiles/Makefile2:202: recipe for target 'CMakeFiles/run.dir/rule' failed
make[1]: *** [CMakeFiles/run.dir/rule] Error 2
Makefile:170: recipe for target 'run' failed
make: *** [run] Error 2
zeb@kutta:~/deal/examples/step-57> make run