I have had the same 'vertical line' problem as well on my Duo-R. They usually appear on solid blue and purple screens, but are pretty minimal in my opinion. In my opinion, these 'jail bars' do not detract from the quality of the image since they can barely be seen. I believe it is inherent to the RGB mob, because I never saw those lines while playing in composite(my RGB-modded N64 also has this problem). S-Video modded units also have the same problem(even moreso), so don't go there if you expect to rid yourself of the vertical line problem. Also, an RGB-YUV transcoder will not get rid of this problem -there is no such thing as magic! Even with some of the problems we must face with RGB-modded systems, it still looks far better than composite video will ever look even on its best day! I hope this is consolation for anyone that may be seeing an image that is not completely perfect...
Erik