Howdy,
I got the same message connecting my iPhone while running High Sierra.
It looks like it installed some software to allow iTunes to talk with the newer iOS on the phone.
What is the exact error you get during the install?
It installed and worked for me, so maybe try:
- Make sure that your software on your Mac and iTunes are up-to-date.
- Quit all apps (especially iTunes) and see if it installs.
- If you can connect to Ethernet, try booting into Safe Mode and see if it installs.
That is to see if some other software is getting in the way of the install.
- Setup a "Test user" and see if the software will install while logged into that user.
ivan