>A machine has Windows Live Messenger 8.5. When signing in it indicates a new version is available which you can choose not to install but then you cannot sign in with old version. So you accept installation and what happens: installation is aborted without explanation after 75+% progress.
>
>What can be the problem? I logged as user with administrator rights.


I ran into the same situation. I uninstalled all Windows Live components and downloaded a fresh installer from their website and ran that. Then, the installation worked fine and everything is now working as expected.

Jon