Unable to install Windows SBS 2003 SP2

I'm running Windows Server Small Business Server 2003. For months I've been unable to install SP2 because I get the following message "Unable the verify the integrity of the file update.inf".

I've worked through numerous procedures listed at Microsoft, like checking the Cryptographic Service, renaming Catroot2, unregistering and re-registering DLL's. The document I used had about 10 steps.

I've also downloaded SP2 manually and got the same results.

I did read one article that talked about installing Windows 2003 Server SP, then Windows 2003 SBS SP, but I didn't want to get into that before understanding this better.

I have heard that it could be related the hot fixes, and there must be al least 60 hot fixes on this server.

Thanks