I'm pretty sure that that's simply how it's choosing to display it there... but that doesn't explain why it's not accepting it as a valid key for activation. Isn't Windows RT supposed to come pre-activated? I believe that my Surface RT did. Is the VivoTab RT different? Does ASUS give you instructions to activate and the key to do it with?
I would follow the instructions here
to get your product key and input it into that screen that you screenshot. Maybe it'll accept it then.
If that doesn't work, then maybe there's something that you forgot to tell us... like you re-installed Windows RT, performed a recovery, tried to change product keys or something like that. Unless you clarify, we have to assume that you just unboxed a new VivoTab and this is what greeted you.