Ciao Francesco, can you please tell me what you get in a shell if you type g++ --version c++ --version clang --version Then, open the file madgraph/iolibs/export_v4.py go at line 1490, it should be at the beginning of the replace_make_opt_c_compiler function and put a print 'COMPILER', compiler line, with the same indentation as the following line which should be p = misc.Popen([compiler, '--version'], stdout=subprocess.PIPE, stderr=subprocess.PIPE) then can you try to re-generate the process and tell me what you get at the end of the output command? Thanks, Marco Marco Zaro On Sat, Jan 24, 2015 at 12:47 PM, Francesco Giuli <