Windows Installer uses the registry to record information about updates installed for each Windows Installer-based product. These registry keys help identify the state of each update: registered, applied, superseded, or obsoleted. Information about installed updates is stored across several registry keys and values. To allow for the product to be in a serviceable state in which it can be repaired, updated, or uninstalled, it is critical for the data in these registry keys to be synchronized. When the data in these registry keys is no longer synchronized, maintenance mode operations cannot be performed on the product .msi file.
The Patch Registration Cleanup Tool helps resolve some issues that are related to invalid or corrupted update registration. This tool lets you bring the product back to a known state so that you can reinstall updates.