The "Administrator" installer for Skyline-daily installs itself in the "C:\Program Files\Skyline-daily".
External tools do not work very well with this type of install of Skyline and Skyline-daily.
In order to install external tools, you have to run this Skyline-daily as an administrator, but, also, when you do install a tool, other non-administrators who run this Skyline-daily will not see the menu items that have been added to the "Tools" menu.

If you would like to use external tools with Skyline or Skyline-daily, we recommend that you use the regular installer, which installs Skyline-daily somewhere inside of your home directory.
Alternatively, you can use the "Unplugged" installer which involves downloading a .zip file.

Regular Skyline-daily install page:
https://skyline.ms/project/home/software/Skyline/daily/begin.view

"Unplugged" Skyline-daily page:
https://skyline.ms/wiki/home/software/Skyline/daily/page.view?name=install-disconnected-64

-- Nick

Dear Nick,

Thank you very much for your reply. I tried your suggestion of downloading the regular skyline (23.1 version from the home page of your website) but now when I try to install MSstats I get the message :
'Failed attempting to extract the tool from MSstats.zip
Specified file not found'
I also tried the installation from the .zip file that I downloaded, without success.
As for other tools like Prego, the installation worked fine, but for AvantGarde it could not install two R packages (stringR and ggplot2) which however are already present in my computer.

Thank you very much in advance,
Giovanni