//System/Library/Extensions/AppleUSBEthernetHost.kext

This alert came up when I installed the latest iTunes update on my iMac. I am running OS 10.9.4. I too have no idea how to reinstall it. The same extension is on my macbook, also OS10.9.4, but it showed no alert when I did the same iTunes update.

This page suggests that it's to do with tethering for iPhones and indicates a test routing:

http://blog.iphoting.com/blog/2012/09/04/fixing-broken-iphone-usb-tethering-on-o s-x/

(If you run his test don't include the $ at the beginning).

I saw this error message on 10.6.8 when installing the latest iTunes update but running his test comes out OK so I suspect that it's a glitch and can be ignored. Until you find that something actually isn't working I should take no action.

I've been busy looking around other responses and found a fix. I downloaded the latest iTunes from the Apple site and installed it. At the end I got the alert again about the kext file. Then I went to the System/ library/ extensions folder and put the AppleUSBEthernetHost.kext file in the trash. Next I ran the iTunes installer again. This time there was no alert only "the application was installed successfully". When I looked in the System/library/extension folder there was a new AppleUSBEthernetHost.kext file there. Hopefully all will now be OK. Thanks for your interest.

Thanks brianfromforfar, this is exactly what worked for me as well. Easiest solution unless/until apple releases a patch?

go to https://www.apple.com/itunes/download/ , or search for iTunes for mac download (from apple.com), click the download button and save to your mac.

in Finder go to: your hard drive that OS X is installed > System>Library>Extensions>AppleUSBEthernetHost.kext , or search for AppleUSBEthernetHost.kext in the System folder via Finder, and delete it.

now install the downloaded iTunes 11.4 .dmg and it will replace the deleted file with an updated file, resolving the error.

Many thanks for the solution, it worked perfectly. I was nervous I might lose stuff but it's all there. Thanks again.

Hello everyone,

I am getting the same "//System/Library/Extensions/AppleUSBEthernetHost.kext was not installed properly and needed to be reinstalled" message, but while I am trying to install a generic postscript printer drive! And of course, I am not being able to complete the printer installation. Any thoughts? Help is much appreciated.

Thanks to you both, this fix worked for me too, after long ignoring the error message and vainly waiting for Apple to get around to an update.

Then last night I lost my Internet cable connection, which uses Ethernet between the modem and my iMac (Max OS X 10.6.8). At first, I blamed my ISP because the modem played up for a while, but after I rebooted it a few times, it returned to normal, but I still couldn't get online. I suspected, rightly or wrongly, that this faulty kernel extension might be the culprit. It took me 90 minutes' fiddling to obtain a slow Internet link, but that enabled me to download iTunes 11.4 from Apple.

I cautiously created a "Pre-trash" folder in which I dumped the non-functioning AppleUSBEthernetHost.kext and a back-up of iTunes library files before using the iTunes installer, with an eye on the open //System/Library/Extensions finder window. When the new kernel extension popped up in it towards the end of the installation, I noticed that it bore the date July 29, 2014! Its predecessor dated from mid-2009. This is not the first time in many years that an iTunes upgrade via Software Update has caused problems, usually corrected by downloading directly from the Apple site.

I fixed permissions for good measure and have found that my Internet connection is also nice and fast again, but I have no idea whether that's pure coincidence.

Other than trying to search for the AppleUSBEthernetHost.kext file itself somewhere on the net and manually replacing it, you could try using the same fix we gave re: iTunes. Despite the fact that you're not seeing the error during using or installing iTunes, it should still be a sloppy way to update the AppleUSBEthernetHost.kext file you're having trouble with. See the steps given previously, but essentially search for the AppleUSBEthernetHost.kext file in extensions, delete it, and install the new iTunes dmg. It shouldn't hurt your system and still give you the latest AppleUSBEthernetHost.kext file… Of course back up first, and then download the iTunes .dmg before deleting the kext file from your extensions folder 😉