Similar situation to me. iTunes 11 (OSX 10.8) failed to install IPA file. Everything seems all right, but there is no app on device, iPhone4 iOS6.0.1 in this case.
But when I install app via Test Flight, installation works.
When I try to install same application on OSX 10.7, iTunes10, installation works fine.
Maybe is problem in iTunes artwork that has to be 1024x1024, I do not know.