I've created a PNG version of a document that I made in Illustrator. The PNG seems to have a couple inches of white space next to it. I have checked for artifacts to the side of the doc. Nothing. I don't have any hidden bounding boxes or clipping masks overhanging my artboard. I even created a new blank document and carefully copied the body of the work and pasted it into the new document. The space is still there in the new PNG. What could be going on that I've missed?