I don't know what kind of hardware and whether or not this is a stack or a chassis but this should explain it better. I would recommend upgrading to the recommended version of code according to the article below:
Please keep in mind that the message is cosmetic so you can leave it and there should not be any network related issues. The message can also be removed from the logs through configuration.
The article specifies 15.4.2 or higher. The recommended software will probably be 15.5 something. I would recommend upgrading to remove the log message.