OK for the sake of argument I moved my Interface and WTF folders out to the desktop and deleted the contents of my Cache folder. I then loaded up WoW and created 20 new toons (10 allies and 10 horde) on 10 different servers . After entering the game with each toon and setting the interface up I exited WoW and installed nUI (Plus) 5.06.10 and CensusPlus 4.2.2.
I then logged back into the first toon and the screen was blank, no error just blank screen. I logged out and back in and everything was fine.
I got the same error (blank screen) on my sixth login(third server). I don't know if it matters but both toons were night elves in shadowglen. First one a Hunter the second a Warrior.
I then proceeded to run a census on all ten servers twice, giving me a total of 40 different logins throughout the night. I didn't have any more trouble after those first two blank screens on servers 1 and 3.
Below are screenshots of the blank screens. Notice that on the first server that the Census Plus Button Icon is not yet loaded around the minimap and in the second screen shot it is there.
I will try to get more logins in tommorrow and see if I can replicate any more of the errors I was getting before.