That's what I have in place. It doesn't work.
If the Check New Username fails, a message is displayed because I have a url parameter attached to the failure redirect. However, if I try another username, that I know doesn't already exist, but the Server Validation fails this time, the Check New Username error message is still displayed.
I've even tried adding the same url parameter to the failure redirect of the Server Validation, but with a different value, but it just appends to the URL so that both parameters are true!
Urggh. What am I doing wrong (again!)? :( See attached and link below.