I had this same error message for days and finally figured it out.
I had somehow gotten a my.cnf file on my computer from AMPS or possibly
another MYSQL install (that I believed I had deleted).
But it turns out it was a hidden file in /etc/ that I had to manually
Finally, I installed MySQL with homebrew one more time –– and
success! It works. Also of course this time I spot a message in the
homebrew setup process that points out the problem I was having:
A "/etc/my.cnf" from another install may interfere with a
Homebrew-built server starting up correctly.
Hope this helps.