reference 'm_cost_function' cannot be declared 'mutable' [-fpermissive]

While compiling nestk on a Fedora 15, I have the following error :

nburrus-nestk-fcd2984/ntk/numeric/levenberg_marquart_minimizer.cpp:66:25: error: reference ‘m_cost_function’ cannot be declared ‘mutable’ [-fpermissive] [ 62%] Building CXX object ntk/CMakeFiles/nestk.dir/numeric/differential_evolution_solver.o [ 63%] Building CXX object ntk/CMakeFiles/nestk.dir/numeric/differential_evolution_minimizer.o make[2]: * [ntk/CMakeFiles/nestk.dir/numeric/levenberg_marquart_minimizer.o] Error 1 make[2]: * Waiting for unfinished jobs.... make[1]: * [ntk/CMakeFiles/nestk.dir/all] Error 2 make: * [all] Error 2

Gcc version :gcc version 4.6.1 20110908 (Red Hat 4.6.1-9) (GCC)

rgbdemo / nestk

reference 'm_cost_function' cannot be declared 'mutable' [-fpermissive] #4