I mean delete the xml file. It'll be recreated whenever you start an addon that uses metahandlers.
You need to physically create the directory structure (the metacache, tvshow and movie folders) inside your destination folder. You may not be able to install metapacks from the ipad for the same reason. The easist solution is probably going to be to install xbmc on an actual machine, then use it to setup the shared folder and install all the metapacks. Once that's done, just point the ipad to the folder (you can even uninstall xbmc from the machine if need be)