I upgraded from Zbrush 4 r3 and no longer was ztl files associated with Zbrush. I could not manualy associate them as windows dont list Zbrush as a assignable application for file types, this means it didnt regester with windows correctly. I completly uninstalled Zbrush and installed R4 as stand alone installation, and again Zbrush is not registering with windows.
Iv never had this issue before. Im using Windows 7 64bit
Thanks.