Hey Lux, as predicted it's the special character that's causing issues in this case. It was something that we accounted for the beta registration page, but forgot about here.
I've added a fix to standardise the two which will go live with the next site update.
With respect to this we'll need to username a little so it meets the site conventions. I've changed it to
Lux AEterna for the time being. Are you happy with that, or is there another tag or variation you would like?