Originally Posted by BMXTRIX
Well, a facing tool is definitely expensive, but many shops have facing tools in house and may be able to do something. I wouldn't expect this to be the case as decent cranks should come properly faced.
Most often the sprocket is slightly out of round, or it is off angle slightly.
Right, thank you. I don't think I was clear enough on order of likelihood...a sprocket out of round is the #1 culprit for a thing like this, most of the others are pretty remote (but not unheard of).