I already have Preference (child and parent) installed one of my test sites but when I try to install Preferential I get this notification: Unable to create directory uploads. Is its parent directory writable by the server?
I tried switching the live theme to Twenty Thirteen and tried to upload Preferential (parent) again but I still get the same notification.
That will be something related to your WordPress…If it says “Uploads” as not being created, it also sounds like that directory (folder) does not exist. Check your site files and make sure that is there, but if not, manually create one.