Office (and many other programs that use the Windows Installer Service) will often prevent reinstallation and uninstallation if there is a version conflict. This is how to correct this problem.
Programs that use Windows Installer Service are very picky about version conflicts.
Here is a common example. You install Office. It works well but something gets corrupted. You've lost your disc so you rebuild off the network or try to update online. Maybe you try to upgrade to the latest version. You get to a point that you can neither reinstall or uninstall and receive an error like one of the following:
This patch package could not be opened. Verify that the patch package exists and that you can access it or contact the application vendor to
verify that this is a valid Windows Installer Patch package.
This action is only valid for products that are currently installed.
Setup is unable to remove earlier version.
The feature you are trying to use is on a network resource that is unavailable.
Error 1612. The installation source for this product is not available. Verify that the source exists and that you can access it.
This is a very common and painful problem that is caused by the Windows Installer Service. The best solution is to use Windows Install Clean Up to blitz the previous installation. After you "clean up" the previous install, you will be able to reinstall the program that is giving you the problem.
The Windows Install Clean Up program is powerful and can be dangerous. Read the support article noted below before running it on your system.