This is a pretty funny and drama-filled thread. Unfortunately, the original poster has edited out most of his posts.
Basicly what happened:
1. Some of the members of said horde guild were invited to help with the Eranikus world event, but instead of helping, took it upon themselves to kill the alliance healers who were flagged from healing the main NPC.
2. At a later date, one level 46 warrior from said horde guild decided to attack Emeriss when the alliance guild was pulling him, greying him out for the alliance guild, and wiping some of the raid. For those of you that have never fought Emeriss before, one dead person can wipe half of of the raid when they turn into a mushroom and kill people around them.
It's getting pretty long, but still a good read. I can't believe that these people could be so stupid.
http://forums.worldofwarcraft.com/thread.aspx?FN=wow-realm-muradin&T=5661&P=1