How to fix "macOS needs to repair your library to run applications" after High Sierra upgrade?
So none of the given answers works on High Sierra (OS X 10.16.x) and I don't have Clean My Mac 3. This Apple article did the trick for me and pretty easily: https://support.apple.com/en-us/HT203538.

This involves setting the permissions through the finder and then resetting the permissions by using the command

diskutil resetUserPermissions / `id -u`


Make sure you cd to the appropriate home folder (I did this logged in as myself for another user that was experiencing the issue) to avoid access errors.