This issue was originally raised here: https://forums.elderscrollsonline.com/en-gb/discussion/601739/character-creation-save-failure#reply-anchor
But it was never answered and just swept under the carpet.

However I am also having this issue - I can create my character on one account but when I delete that character and try to use that name on a new account I get the Save Failure error - this is clearly a conflict in the backend that needs to be resolved.