Try installing in local a brand new tiki 3.2, and compare the mysql table users_users (columns, etc.) with the one in your server. There is something different for sure in your upgraded db (maybe you were missing some step in a previous upgrade process or some problem occurred). But normal upgrades from 2.latest work fine (I've done several in different servers without that issue at all)
That could be easy and fast to fix with some patience using phpmyadmin or similar to compare both tables and fix the wrong one.
Or you can request help to one of the Consultants to do it for you if you don't wat to do it yourself.