You will see that I have a white line on the right hand side of the header. Not sure how I did that. Also, a couple of the bases for the sponsor boxes are misaligned - although I will turn those off once I figure out how... so no big deal.
If you are talking about the little tiny think white line (on IE) it might come from your tagline padding. Try to give it a little less padding from right and see if that does the trick.