OMG, I have already answered one of these today. It must not be me, it must be a vBulletin problem....
Anyways, I emailed vB tech support about this issue, because some of my users and myself were having this problem.
I had to make it "AdminCP "-> "vBulletin Options"-> "Messaging and Posting Options" -> "Quick Reply" -> change to "Yes, Click not Required." It works now, but I would like to activate it by clicking. oh,well...