I´m getting this error in XCode:
2013-08-23 14:36:18.284 Tell The DJ[14955:c07] ERROR: Plugin \'Device\' not found, or is not a CDVPlugin. Check your plugin
i think you need to use the correct config.xml for me, it is Xcode project target folder config.xml, and not platform www folder
This can also happen if you have a plugin that is referenced but not installed. If you have tried the above solutions and can't find the referenced plugin's .m file it might be that the plugin isn't really installed.
I would check your plugins directory to be sure that there are files in it. If not, reinstall the plugin. I ran into this when I had a typo in the git repo when restoring plugins from the config.xml.