After reviewing QuestHelper's code and skimming through WoW changes, QH is looking for the function
WatchFrame_RemoveObjectiveHandler, which was removed in Patch 6.0.2 along with entire WatchFrame.lua file. Quest tracking was then rolled into a new
ObjectiveTracker, which became a separate "addon" inside the interface code.
Given that QH is looking for three specific functions as a failsafe to protect against private servers, I'm assuming those three functions weren't available in Wrath and earlier and are necessary for the addon to function. Since one of them is missing now, QH probably won't work even if you disabled the private server check.