The Microsoft Official MSI Fix
If for some reason you are unsuccessful with either of the above suggestion, there is another method you can try, this time focusing on the cause of the problem, the Microsoft Installer issue.
According to Microsoft this is caused by a conflict with the Customer Experience Improvement Program (CEIP) and causes Explorer and MSI-based installers to fail. It should only affect Windows 7 beta users, but there is a chance that the problem may persist in the release version.
To resolve this conflict, go to Start and type cmd in the Search box. In the displayed results, right-click cmd.exe and choose Run as administrator. Agree to the User Access Control warning and the command prompt will open.
At the prompt, type or paste the following:
reg delete HKLM\SOFTWARE\Microsoft\SQMClient\Windows\DisabledSessions /va /f
Press Enter to run this command. The registry key that causes the Customer Experience Improvement Program to conflict with MSI files will then be deleted, and you will be greeted with a message:The operation completed successfully.