It his very useful to provide a valid repair path to an MSI software in order to allow automatic repair capability of Windows Installer.
Here's where to go in your registry:
Select your software key: Ex.\Products\1C5C0DF1B10BC4B469705E3D3B1D13F8
Go in this subkey: \SourceList\Net
Then add a path in string "1" where the MSI can be found:
Ex.c:\program files\microsoft intellipoint 4.1\mouse\Setup
Windows Installer automatic repair capability his now enabled for your MSI software.