Thanks for solutions from Jazzmammal and Andrew...
Now day time in Germany, I'll check this evening...
I use Windows 7-64bits and of course, I have set the
Amplitube at 64 bits accordingly, but I did not come to the idea
of installing both 64 and 32 and to install them in 2 different
files (perverse!). You never stop to learn!

Concerning the administrator topic, I know understand (It will
be the hope I will be living on today until I can check it)
that I have to start Windows (booting up) as an administrator.
I am not sure how I do that (thought you could only do this for
a stand alone program) but it will keep me busy this evening!
Thanks to all helpers, it's a hard world!