"For those with access to the (iTunes) 11.3.1 installer, you'll notice when running it (by selecting "Installer Log" from the Window menu and setting the Detail level to "All Logs") that a number of components are skipped "because the version [newer] is already installed."
In order for all of the 11.4 components to be replaced, in addition to /Applications/iTunes.app, you will need to remove:
Having done that, and re-running the 11.3.1 installer, the buggy 11.4 version will have been removed and 11.3.1 restored.
There have been many problem posts on iTunes 11.4 (see earlier FYI below). I don't know how many had or tried a restore from TM backup instead of the above. But posting it regardless as it has been useful to others that regretted installing iTunes 11.4 and found reinstalling 11.3.1 didn't help due to later files not being overwritten by the older iTunes installer.
"About iTunes 11.4
(link disabled as same page URL is used for later iTunes updates)
iTunes 11.4 now supports the ability to sync your favorite music, movies, and more to devices with iOS 8.
File Size: OS X (242.92MB), Windows (111.3MB), Windows64 (112.8 MB)
- OS X version 10.6.8 or later
- 400MB of available disk space
- iTunes in the Cloud, iTunes Match, iTunes Radio availability vary by country
- iTunes Radio requires OS X version 10.7 or later
- iTunes Extras requires OS X version 10.9.3 or later"
FYI: There's several threads in Apple's forums about an AppleUSBEthernetHost.kext (extension) related error message after updating to iTunes 11.4:
"System extension cannot be used
The system extension "//System/Library/Extensions/AppleUSBEthernetHost.kext" was installed improperly and cannot be used. Please try reinstalling it, or contact the product's vendor for an update."
Example thread links, some with tips (usually deleting the extension and then reinstalling iTunes from a download installer (link above):