This is much better!
Indeed, I followed the counsel and created a brand new workspace, project, and only dropped in it all the files I had.
When I saw it running... fine! But is it really the icon?
I used the icon, and it worked fine!
Then I played with the other target settings and finally found that the guilty one is "Embed Project .UIRs".
I'd like to have an NI comment on this.
Anyhow, thank you Siabevef, and...
Ciao (I'm Italian)