Yep. My group's been down for about a year due to one of these "new world" recommendations.
Fortunately, we just came back on the 1.6.4 beta, so we're set for a little while, but it'll come again.. I think the only real way to resolve is for there to be some sort of conversion tool. I remember with some of the old Technic migrations, users created a worldconverter. Without something like that, we have to reset.