The Spirit Realm

Last night we tried to do MPG: Specialization with one group. Unfortunately we were able to get the instance, but we could not get the npc live. We kept getting a message saying "Without mustering a larger party here, you have no chance. Return to me when you have assembled your forces here in the arena". Did we get hit with the bug bat, or is there some secret minimum number to this? I was under the impression they had lowered the minimum requirements, but what good is it to be able to get the instance if the numbers won't let you execute the script?