Nui in Zul'Gurub
 

I was in Zul'Gurub using Nui version 5.03.05_dev and was unable to interface with the raid. As long as I was in the dungeon, I could not click to trade, whisper, put up raid icons, etc....

When I left the instance it was fine.

very strange.

This issue is most commonly caused by Cartographer or another mod and is unlikely to be an error in nUI.

I think quest helper was another cause but if you look on the wow forums you'll find lots of people with the issue who do not use nUI

This was also caused by Perl Unit Frames.