Windows Installer won't let me install

Trying to install a Silverlight Update, a Java update or other software, I get this window:





What could be the problem ?

Go to Control Panel | Programs and Features and uninstall Silverlight entirely, then go to microsoft and download the silverlight package and install it. I have had to do this a few times already, and it is annoying.

The same goes for the Java 6 Update 18.

If I try to uninstall it it shows me the same window as in the first screen. I don't think the problem is with Silverlight, because I get this with other software too.

Go to Microsoft Corporation and download the "windows uninstaller cleanup tool", where you can remove the offending software from the Programs and features. You should be able to install them again after that.