I had a similar issue today. Some of the Bestop Protectant dripped down onto my vinyl windows and now I can't get it off, either. Some also dripped down my windshield and I literally had to scrap it off with a razor blade (and it still didn't come off easily). Obviously, that's not an option for the vinyl windows.
The instructions on the bottle do say to not get it on the vinyl windows but I would expect a stronger warning given that it apparently bonds to whatever it comes in contact with--how about something like: "If you do get it on, it's never coming off."
Like bierbrewer, if anyone has any hints as to how to get this stuff off the vinyl, I would love to hear it.
I certainly expect more from a company like Bestop.