Try this. Get an iPad you’ve not tried to install onto before. Go through the process of getting it registered for deployment. When it comes to installing the app on the iPad, don’t copy the file anywhere, don’t load iTunes. Plug the iPad into your dev machine and try to install the .app onto it using XCode, not iTunes. If that works, try the same with one of the devices which is already registered in the certificate. I always have problems if I have not registered the device in XCode with the “Use for development” button (now on the drop down menu in XCode’s Organiser window.)
eg:
Try this link, it’s a bit old now, but should be relevant:
http://ofps.oreilly.com/titles/9781449389765/appa.html [import]uid: 8271 topic_id: 24620 reply_id: 100247[/import]