lynksseus on 08 September 2016
From what I recall, Wii U regardless of its storage capacity, you can only accumulate a maximum of Wii U 300 "channels". Do you actually have 300? From what I understand, this includes useless channels or icons like demos, etc.
Delete an icon with the smallest size, with the least amount of play and you should be good.
Edit: Just a guess, btw.
