Some reason Kate is not letting me modify my deck. "This not possible as you do not own this character".
Had the same problem just now - you can change it from the in game screen though!
This might sound silly, but what do you mean?
That didn't work either, but on the game screen click 'My collection' in the game itself. Not the tab on the top of the page.
I think I fixed it! I did by accident, but I accidently cheated...
I used this deck deleted in a game of standard and I lost...
Some reason playing standard using a non-standard deck fixes it. I didn't cheat on purpose (I only played one battle)but what if other people come first in tourneys by cheating? Better fix this soon moderators.
There was some minutes of a delay in it, but yeah. It fixes it eventually, but not right away.