iTunes stuck on "installing" when installing .ipa files
It is very uncommon to download / install a IPA file - free of charge or not.

The IPA files are usually used for known &amp; registered devices (e.g. beta testers) - if your device is not registered and your device is not included in the IPA profile file, then installing the IPA file will fail.

This is kind of the Apple philosophy / protection: either you have a "deep" contact to the developer who includes your device (maximum is 200 devices as far as I know), or you jailbreak (?) your device, or you use the official AppStore and trash the IPA file.