Seems very strange, did you say that you could open some VOBs OK in premiere? What happens if you get a video DVD (ie a commercial film you bought) and drag a VOB off that? Can you pull that into premiere?

Where did this VOB come from? A DVD? Could the problem maybe be something to do with CSS encryption?

I would say ask on the doom9 forums maybe? However you have to wait 5 days after signing up to post.