If I use use "Run>Equinox Framework" it works without problems of course.
I tried instead to launch 'org.eclipse.core.runtime.adaptor.EclipseStarter' directly from Eclipse (because I wanted to understand how Equinox is launched). I fixed the problem manually copying "META-INF" content into output directory of the IDE/Compiler. Previously it failed because it was unable to find
Manifest.fm of System Bundle. Now it works. I know it's not the right way to launch Equinox but is the only way to understand it better.