If Visual Studio 2005 Service Pack 1 fails to install, you might find additional .msp files under %WINDIR%\Installer for each failed attempt. You should not simply delete these patches, however, because if one of the patches was applied successfully to one target product, deleting that patch will cause future maintenance installs – including repairs, patch install, patch uninstall, and even product uninstall – to fail.
After safely identifying orphaned patches, you can delete them. There are a couple of different ways to identify orphaned patches.
If you have the Windows SDK or the older Platform SDK installed or are willing to install either, you can use msizap.exe to identify and remove orphaned data files such as patches. Run the following command. You will find msizap.exe in the bin folder of the Windows SDK or Platform SDK installation directory.
If you don’t want to install either SDK just to get this executable, you can determine which patches are registered and applicable and delete extra patches you find under %WINDIR%\Installer. I have attached a simple script to identify which patches are registered – those patches you should not remove.
To successfully install the patch if you are having problems, please read about known issues with Visual Studio 2005 Service Pack 1 and available workarounds.