While upgrading a PC from SP1 to SP3, I got the error message: “Service Pack 3 Setup Error” “Unable to read from or write to the database”

At first I thought the SP3 upgrade file had become corrupt. But no: I still got the problem after a re-copy.

After a lot of searching around, I eventually found: http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=3265601&SiteID=17

From that site, I found I needed to download a script from: http://www.andrew.cmu.edu/org/hc-tools/files/cryptoxpfix/8-30-2004/readme.html

The fixdb.bat file was exactly what I was needed. After running fixdb, SP3 installed without a hitch.