I kinda doubt that you've got the wrong headset, there aren't that many combinations that'd fit together just a little bit wrong. OTOH there's a small wedge-shaped ring that goes in between the top race and the steerer tube and can easily get lost in a disassembly. If that happens you get what you describe.
Judging by the pic it looks like you might have one of the integrated/semi-integrated headsets. If you get yourself a vernier caliper and take a look at this link: http://www.sutherlandsbicycle.com/Chapter12.pdf
, you should be able to figure out what it is that you've got.
There's a bunch of "Ritchey Logic Zero"s, with a few different dimensions to choose from. Might be that your best option is to hand the bike back to the mechanic and have him order a replacement for you.
Last edited by dabac; 09-08-10 at 07:09 AM.