We encountered the same error recently on a number of XP virtual machines. After a LOT of digging, it was discovered that some of the workstations did not have all of the trusted root certificates that are required.
There is a Microsoft utility that you can run that will ensure that all required root certificates are there:
http: //download.microsoft.com/download/2/9/A/29ABCE61-CF08-46E7-B794-D359B01E72CC/rootsupd. exe (remove extra spaces after http and before exe to turn it into a real URL).
After this utility was run, everything installed successfully!
Hope this helps others that have run into this situation.