Task Not Refreshing as Complete

Noktis

I completed Instance: Sneak Attack Human World before I accepted the task to defeat the first enemy in that area. Now I have beaten him innumerable times yet the task does not refresh as complete, nor do any new ones become available, and the usual highlight for a task target is not indicated on this stage marker. I was told before that it would reset, and although the instance itself has no trouble doing so, the task and target highlight do not, regardless of whether I reset it manually or beat the entire area and wait until the following day. I appreciate the information which was passed on to me thus far concerning this issue however, it has not remedied the malfunction. I have tried everything from switching the difficulty to exitting and restarting my computer, to no avail. As it stands, I cannot access any further tasks because of this. PLEASE HELP