Headset not screwing onto forks correctly

I'm trying to install a new headset, using a 1inch ultera threaded headset. It fits but then when i screw it on i get about 1/2 an inch onto the fork it seizes up and i cannot tighten anymore. i'm using a large park tool wrench so i'm getting more than enough torgue on it but it won't keep going. I've tired:

1. undoing it and cleaning the thread
   
2. putting it in the freezer (thought it might shrink metal)
   
3. force
   
   

should i invest in a real headset wrench or is there another solution / issues that i'm missing?

any help much appreciated.