Qdabra's Query Builder InfoPath form tool needs to run with full trust so that it can execute shell commands. To install this full trust tool on your local computer, we use InfoPath’s built-in support for URN based solutions. When the form is installed, InfoPath adds entries to your Windows registry. Unfortunately, due to a bug in InfoPath installer, sometimes uninstalling doesn’t work and the registry entries are not cleaned up correctly. In such cases, the result is that you can’t re-install the tool, since your machine will think that "The form is already installed on your computer". You might also find that you are unable to remove the form from the InfoPath cache when you run the command Infopath /cache clearall.
If you encounter this issue, try to remove the form using the Windows CleanUp Utility. In addition, you might need to manually clean up the registry. Do this at your own risk and backup your registry before proceeding. If the problem is happening with the QueryBuilder form, for example, search for "QueryBuilder" in the registry and you will find a key like this:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\InfoPath\SolutionsCatalog\urn:schemas-microsoft-com:office:infopath:Qdabra-Query-Builder:-myXSD-2008-02-19T23-06-28.
Remove this key manually and you will then be able to reinstall the form.
Note that this could happen with any installed form, not just the QueryBuilder form.