Solution: MySQL Master-Master Replication Fails With ERROR 1200 (HY000) on Master

When you try MySQL master-master replication with two (or more) servers you may often find that in the process of configuring the original master to also act as a slave server (start slave), it fails with the following error:

mysql> start slave;
ERROR 1200 (HY000): The server is not configured as slave; fix in config file or with CHANGE MASTER TO


To rectify it locate and delete the master.info file and restart the mysql server. Now try to start slave and it should work. In short on my machine I did:
rm /var/lib/mysql/master.info