So back when I had it on my D70 and before my D70 went out I noticed the lens would focus oddly so when my D70 had the "Err" issue I was unable to really see if it's the lens or the camera and now that I have a D200 now I put the lens on and it wont focus at all.. However when I put my "Bigma" on I have no issues with the lens focusing.
Sounds like a lens issue?

