Yeah, there is a problem with QuestHelper. It seems like as soon as you interact with any quests in Dalanis it breaks. I had no issues using it before questing in Dalanis.
On the topic of Dalanis the map there is bugged as all hell - your character pointer not displayed on the map, it commonly has ghost quest markers and follow/search function not working when you are inside Dalanis.
Getting this error most of the time: