There are no instances of an installation on the computer, but this error is thrown when the installation is executed.
This normally happens when another setup on the system was installed with the same Product Code, but with a different Package Code. This would typically happen if after running your setup for the first time on a computer, you modify your Express project, rebuild the release (which generates a New package GUID), and run it again on that system. At this point, the MSI engine expects you to go to the Add or Remove Programs applet to uninstall the existing version of your product, and then install the new package.
Run a minor upgrade of the setup to update the existing setup on the computer. To do this, run the updated setup package with the following command-line arguments:
This will start you install process over.
Notification Server 6.0 SP3
SQL 2000* SP3