Ok, so I'm trying to install Symantec Endpoint Protection 11 on my mothers computer, and I'm receiving the Windows Installer Error 1620, which reads "ERROR_INSTALL_PACKAGE_INVALID: 1620: This installation package could not be opened. Contact the application vendor to verify that this is a valid Windows Installer package."

I've installed this program on a handful of computers and have not had any problems prior to his particular computer.  Any solutions that might help?  I've already installed the most recent version of Windows Installer and it has not helped.