MySQL 5.5 errno: 150 “Foreign key constraint is incorrectly formed”

Question

There are plenty of questions regarding this error but I can\'t seem to find any similar scenario to what I have.

My 1st table (users):

My 2nd table

Answer 1

Since the columns are of the same type, it's worth to check the engine type as @Tim Biegeleisen suggested.

Changing engine type fixed the issue.

ALTER TABLE users
ENGINE=InnoDB;