Sometimes OS X MySQL has some launchd problems. You can run the server but you get all sorts of odd messages when you try to access it via server manager. And you just can't get it to quit properly.
Here's a fix:
go to terminal and run:
sudo launchctl unload -w /System/Library/LaunchDaemons/org.mysql.mysqld.plist
go back to Server Admin and restart mysql
Mysqld should be running fine.