I have a Viking Lily and a similar thing happened to me. The machine was having problems sewing over any seam, it would just sit there and stitch without moving for a bit and then continue (probably with a little help from me). I took it in to a repair shop and explained my problem. While I was standing there, the repair person determined that the feed dog teeth had rounded and did not have the edges to grip the fabric to move it along. He filed the teeth of the feed dogs and my machine goes over seams again.