I get the problem when people sign up well when i try sign up... aswell as that i get the same error with the ajex username and email checker see attached
For me, the error message did not show up in the spot shown in your screen shot, but I did get the same message, right out front at the login position.
I fixed this issue by assigning mod_cblogin to the login module position (at top left under the nav bar at www.yourarlington.com/).
Sometimes, I still get the message when I try to log in, but if I try again, I am successful.