did your quest helper turn off at any time during the quest, especially after defeating Meowority (sp)? If so, it may not recognized that you completed that quest. This happened to me on a couple of occassions. Once fighting Jotun, the quest helper turned off, so I had to do the quest over again.
KI, needs to change the short cut for quest helper from "T" to some other key that isn't used very much, ";" or something.
i did big ben already and i got no error. no i didnt skip and my quest helper was on and i had friends and i made it to the final boss. (there is a secret boss there to. the boss is to spill the 3 milks for the rank 6 boss i believe)