Q: system extension cannot be used AppleUSBEthernetHost.kext

I have the same question: does iTunes 12.0.1 solve the issue with "AppleUSBEthernetHost.kext", that could not be installed before? Thanks

It does, at least on Windows, because I waited a little while to upgrade iTunes on my PC after the disappointment caused by the botched job in iTunes 11.4 on OS X, and since I had a perfectly functioning iTunes 11.4...

Well, long story short, 12.01 works like a charm on Windows (8.1 Update), so it should too in OS X.

I can confirm that the issue is solved on MacOS too! Good thing...

I have the same problem with OSX 10.7.5, so I don't think its the operating system, but the iTunes upgrades. I had the problem for over 6 months now and called Apple Support, paid 19.50 for help on the issue, and after an hour on the phone with them and re installing ITunes twice, dumping the UDB/Ethernet kernel, it still doesn't work. I give up soon.

The latest iTunes 11.4 for OS X 10.6 at:

http://support.apple.com/kb/DL1774

dated: Post Date: Sep 9, 2014

has 242433227 bytes, so I assume it to be a fixed version from the 10.4 version I downloaded earlier, which had 242,940,774 bytes and did not sync my iOS devices.

I think it is either dishonest or sloppiness that the version date on the website does not get corrected, when they are fixing their oversights/mistakes. It's also odd, that when I download the current dmg, the creation date must have been left empty and gets filled by the user's download date, meaning one can't really tell when this dmg was re-created or changed by Apple. There is no change log either.

I was following the tips in this thread to successfully get rid off the error message. However my iOS devices are still not recognized. My bigger problem was that after each system shutdown/reboot, I had to re-install iTunes to get my iOS devices recognized. Apparently some sync-related iTunes 11.4 files go either missing or get changed during reboot.

The latest iTunes 11.4 for OS 10.6 has not changed this odd behavior. 

I've just tried to connect a wireless printer and while downloading the software I got the same message ..and now I'm having trouble with the printer!! Do Apple monitor these forums to see what problems people are having?

I had this problem about a week ago. My computer was giving me the grey curtain coming down saying I needed to restart. That had been happening with some regularity recently. Finally, it would not restart at all. I had to go back and reinstall Snow Leopard (10.6.3) and then run it through every update until 10.6.8. While updating, i got this message at least 3 different times. When I was done, iTunes would not recognize my iPhone 5 or my iPad mini. I found several of these threads on this discussion board. I downloaded iTunes 11.4 and reinstalled it. The problem went away for a day and then the next day it would not recognize them again. Another reinstall of iTunes only and I have not had a problem since then. I read another thread about systematically restoring or reinstalling all your apps one by one. I don't have time for that unless I really have to isolate the problem. I took a chance on my first problem, created a second one that is discussed on this thread, and had a relatively easy, though annoying, fix. I backed up the working version of iTunes so in the future I can replace the defective one from a hard drive.

For me it is "so far, so good" with this fix (~3 days). But what I really want to say is thanks, Trane, for that concise how-to!