ipa file installs in Xcode but not using iTunes.

Hi, I've completed my app update was about to submit to iTunesConnect and thought I'd do an ad-hoc build(.ipa) and add it to my iPhone using iTunes. This has worked fine for all previous versions but it just keeps on failing this time. It says installing, then the icon remains "grated out" even though iTunes seems to think it's completed. When i tap the greyed out icon it changes to "Installing" but does nothing. I then restart my phone and it changes to "Waiting" but nothing happens.

I can download and run the app just fine from Xcode so this only happens when I use iTunes.

Anyone else had this? Is this s app issue or iTunes?

Thanks.