Aditional instances cannot be launched

I've been trying to enter the following instances/raids:
Onyxia's Lair, Wailing Caverns, Shadowfang Keep, Blackfathom Deep, Deadmines, The Stockade, Blackrock Depths and a few more the last days, and always i get the message: -> "Aditional instances cannot be launched"

It happens mostly on the realm of "Doomhammer" i have not been to my other realms to try and enter many dungeons

Some people say that it is because many players are currently inside that same Instance/Raid, but i think that all the Instances/Raids are linked to the same server, which means if to many are playing Ulduar, Naxxramas, Ahn' Qiraj and so on, many players from 10 and up cannot enter any instances/raids what so ever.

If my theory is correct, then i's suggest that you separate the instance and raids into 2 different servers, Or create bigger server Or make it possible for more players to enter the dungeons.

Aditional instances cannot be launched!!!

This message is getting very annoying, and I think that i speak for, maybe not every but most players when i say that Blizzard needs to do something about this.