Can't adjust headset correctly Summary - I'm using an FSA Orbit MX threadless/integrated headset in a brand new steel frame. My problem is that I cannot seem to adjust the headset to the right tightness - either it is too tight and the forks do not turn freely, or it is too loose and there is substantial play/knocking. 

To elaborate on the problem - I'm building up a new bike from scratch. Rather than try to install the headset myself with homemade tools I took it to a mechanic last weekend to have it professionally installed. 

After building the bike up I noticed that the headset was quite loose (a lot of play when tightening the front brake and rocking the bike forward/backward).

So, I tightened it by loosening the stem bolts and tightening the top bolt. That made the play go away, but the fork would no longer swing freely. Loosened a little, and the play returned. I tried for an hour but could not find a middle ground. Either it's too loose or too tight, I can't get it right. Removing the spacers didn't help. The star nut seems to be located properly, a few mm below the top cap. I removed the fork completely and reassembled the upper and lower bearing races and seals, ensuring they are properly seated. No luck. 

It's a mystery. Before I bring it back to the mechanic - is there anything I'm missing?

Edit - some photos of the headset, as requested. Sadly I don't have enough reputation to post more than 2
Mystery solved today. I took it back to the shop and a second mechanic had a look. He suspected that the crown race wasn't seated quite right - it turns out the first mechanic hadn't faced the bottom of the steerer tube and there was a bit of paint there. The crown race looked quite beaten up so he had probably forced it on. The new mech prepared the steerer, re-seated the crown race, and its looking great now. Thanks for all the input.