Installing ad-hoc application hangs on installing

I have developed an iPad application, and added a friend to my provisioning profile and rebuilt my application. I then sent him the .ipa and he has dropped it into his itunes application, and he can see the icon on his home screen but it just hangs on "installing".

Any ideas? Also, he said that the icon doesn't show in his iTunes but it does show in the organizer when i archived the application.

Any help is greatly appreciated.