Instances...

We very much realise how frustrating the message is, and that is why we are actively deploying realm modifications across all realms which will resolve this. I am sorry if this is the first time you have heard we are doing this, but we have been regularly updating the community about this through posts here in the forums and in-game via breaking news.

Here's the main thread, which links to other threads too:
http://forums.wow-europe.com/thread.html?topicId=9941934722&sid=1

If your realm hasn't had this modification yet, please rest assured it will do. It is unfortunately not a simple or fast fix, however. We honestly are sorry you are being frustrated by seeing the "Additional Instances" message over and over again and that is why we are working on it.