Ctrl-Alt-s does not type ß anymore (US International keyboard layout)

In Windows 7 I still use the US International keyboard settings, because I often type in English, German, French, Italian and some other languages.

The settings still work - characters like å, ø etc. are still within easy reach. But with one exception: The German 'sharp S', the ß sign, doesn't work.

The Ctrl-Alt-S or AltGr-S combination that is supposed to make ß, now deactives the window I'm typing in. It will still be full screen but not active. It is not a feature of one program only because it happens both in Firefox and in Open Office.

So it looks like Ctrl-Alt-S is a Windows shortcut for something, but for what? And how do I disable it or make sure my keyboard settings override it?

Thanks. But I don't have MS Word on my new computer.
According to Microsoft http://support.microsoft.com/kb/306560 Ctrl-Alt-S should give ß but on my computer typing that combination makes the current window inactive.

My computer is an HP Phenom x6. I had the very same problem. If you have the same system as I, go to the HP Support Assistant Properties and the Shortcut should read Alt-S. That will pop-up the support window. Delete the Alt-S for shortcut and put "None" in its place. I did that, and now my Alt-S types out the ß just fine.