Vel'Koz has two original skins in teambuilder. Selecting the second gives you an error.
Happened right before I posted this. 2/26/2015 10:21 PM EST
Have verified this multiple times in the same session, but not completely logging out and logging back in. It works if you select the first Vel'Koz original skin.
. I didn't start noticing it until after I got the Arclite Vel-Koz skin.