I experienced this error while trying to utilize PHPMyAdmin to setup a replication process where an Amazon RDS instance was the slave and my master was my dedicated server. The issue here is that the connection was made successfully but that I do not have permission to adjust the slave/master status of the RDS instance. Amazon has confirmed that this is the case. That's unfortunate, I was hoping it would ease our transition to Amazon's services.
The error that PHPMyAdmin returned was "Unable to change master"