Assembly ‘X’ could not be uninstalled because it is required by another application Chances are that your assembly has a pin in the registry which stops it from being uninstalled. You can find these here:* HKEY_CURRENT_USER\Software\Microsoft\Installer\Assemblies\Global* HKEY_LOCAL_MACHINE\Software\Classes\Installer\Assemblies\GlobalJust remove the keys, and you can now uninstall them from the GAC.