Upgrading to SBS R2 after SP2 has been installed. Is it posiable?

I have a SBS 2003 SP2 server that I want to upgrade to R2 but my attempts to uninstall SP2 and install the R2 Upgrade were not sucessful. I kept getting the message that SP2 is installed.

I have tried Konwlage Base to no avail.

Any thoughts?

L