When I backed up my old Runtime I renamed it "Runtime Lifeboat". After I reinstalled Poser, I took the new Runtime directory and renamed it "New Runtime". Then I copied "Runtime Lifeboat" into the same directory and changed it's name back to simply "Runtime" allowing me to switch the new RT for my Old RT while preserving the New RT. What this did was allow me to swap between the 2 directories by simply changing which one was named "Runtime". This is how I was able to determine that one directory works (the new one) and one doesn't (my old one).