Hi, if it of any interest I used to get that with the old version as well. Several releases of Firefox did the same.
I never tried it with IE, Mozilla or Opera.
It only seemed to happen if I minimised AO and opened another browser session. I also had to be out of AO for perhaps 20 minutes or more?
EDIT: There is something weird. It has just booted me and will not show my user ID or any of the private forums. But I can edit this?