Recently I ran into a situation when upgrading from MySQL 4.x to 5.x on a dev box of mine. I actually ran into this a year or two ago too, but I forgot to document it (I know, I know) and so I didn’t remember it. I thought I would post it here now to share with all of you in case you run across it yourself. Once the upgrade was done, the application that connected to the database would connect no longer. I kept getting authentication errors no matter what I did. This was a fresh install, I just imported MySQL dump files for my databases, so I thought it was a setting or something that I had forgotten. I checked everything out and could find nothing wrong with the settings, user accounts, passwords, you name it. The app I was launching ran on Windows (specifically, this is my EQEmu server, check it out daBoneyard), and it’s a console app so the Dos window flies by and I hadn’t seen the error message. Finally I decided to put a pause in the batch file and see what the heck was going on. It was then that I was presented with the following error: