I've occasionally run into this with Mac the Ripper, tho not consistenty. (One note: You ARE going to the "mode" screen before you start ripping, right? If you leave it on the "disc" screen, you'll get all sorts of error messages like the one youmention.)
My most consistent solution is to always to a full-disc rip in MTR and then select titles, chapters or layers to extract and burn using DVD2oneX. It's a particularly simple one-click solution if you just want to burn the main title, which is most likely when you're making a backup for the kids to (ab)use. It always seems to work reliably for me, and the speed depends on how much compression it has to do. If it's just extracting a title, and doesn't have to compress it to fit on a 4.4gb disc, it only takes about 10 minutes on my G5.