I had the same problem with 6U24 update...
My workstations with 6U23 would successfully update to ver 24 once i uninstalled ver 23. My older workstations with ver. 22 would not install to ver. 24. So i tried to install ver 23 but I received the same problem...
My fix is easy and it works everytime. I simply re-installed the VeriSign certs prior to installation, re-ran the install process and it worked like a charm.
Hope this helps somebody out there....