I've seen this several times on other MMO's, where no one can engage a boss or group of enemies. Hopefully it is just a server issue so that simply a server reset will fix it. But, if it's a quest thing it could take longer for them to get it fixed.
We're still taking a look at this quest, but I have heard reports that switching realms may help the situation in the mean time. Can one of you try that out for me and let me know if it's a temporary work around?
Last night I tried switching between the Crowded servers on the first page and those did not work. However, I just now switched to the server Raven Eyes, which as far as I know is always Perfect, and the battle did work. So for anyone who cannot complete it, and to answer your question One-Eyed Jack, the servers which are not very popular are possibly the only ones in which the rat pack may be fought.
I never play in crowded realms, and couldn't get this battle to start. I tried switching realms and it didn't help.
After I posted this I tried again and it worked. I had to switch realms about 5 or six times before it worked. Raven Eyes didn't work for me. I can't remember the name of the server that did work. It just took patience to switch that many times.