Sorry, I correct my previous post:
I can build with success a simple program, but then the error is the same:

BUILD SUCCESSFUL (total time: 2s)
Loading C:/Pbpx/prova.X/dist/default/production/prova.X.production.cof...
Loading C:/Pbpx/prova.X/dist/default/production/prova.X.production....
The program file could not be loaded: java.lang.NullPointerException