Hi Antonio, As you know I had some problems with MSVC 2015 in windows 7. Most of my customers uses w7. I had to back again MSVC 2103 urgently. (Harbour (harbour_3.2_32bits_VS2013_20160309.zip), MSVC 2013, 2013 related old libraries and your fwh 1604 (build zero) libraries for MSVC 2013) I should say...
... have a detailed guide to learn how to do it: http://forums.fivetechsupport.com/viewtopic.php?f=17&t=28723&start=0 Though the guide is for VS2013, it properly works for VSC2015. In fact I have updated it these days as I have been using the VSC2015 debugger too
I have had same Problem! My solution was uninstall vs2015 and all previous versions of vs (vs2013 community and vs2012 express). New install of vs2015 community and now all was ok (vcvarsall.bat and cl.exe is in bin directory). Now all run perfect with fwh1603 - only checked with 64bit.