DL100 G2 upgrade R2 ver from workgroup to standard

[Gordon C Haas]

I've a nice bright shiny new dl100 g2 1 Tb, it came with WSS R2 installed. I purchased the upgrade from workgroup to standard (HP parlance) but whenever I run the upgrade dvd it says 'this server doesn not appear to qualify for the upgrade'. The upgrade dvd is titled 'HP Proliant MS WSS 2003 R2a, wrkgrp ed x32 (1 cpu) to standard edition x32 (1 - 4 cpu) upgrade'

So there's a number of questions:

I'm running a dual core cpu, is this what the upgrade is complaining about?

What's R2a version? Is it not happy because I've got R2?

and finally...

Why won't this work? I've gone back to factory default twice now and it's getting tedious.