An .msi file is a database of all the files, settings, and configuration information for the associated application. When you install Office on your computer, the .msi file is saved in a hidden folder. Without this file, Windows Installer cannot update your configuration, install optional features, or apply software updates. Office cannot be installed, repaired, or updated if the .msi file is not found.
Why is the .msi file missing?>>
The most likely reason for Windows Installer to require the installation CD is because the saved version of the .msi file for Office has been inadvertently or deliberately deleted from your computer. It is also possible that the file is damaged or corrupted.
Occasionally, changing the drive letters associated with partitions on your hard disk can cause this problem to occur — such as changing drive C: to a different letter or moving the hard disk drive from one computer to another. Other possible causes are a damaged or corrupted hard disk or registry file.