However, when I select the update file, I get an error in the GUI that reads "The file may be corrupted or check for the available disk space", and the command window behind it says "SEVERE: ERRError in writing inf.xml file."

I have confirmed that there is plenty of disk space available on the server, and tried re-downloading the service pack several times, and even on different computers. However I always get the same result.

This installation is on a Windows Server 2008 system, but was migrated from a computer running Windows Server 2003. Can anyone tell me what I'm doing wrong? It almost sounds like a permissions issue.