Can't take the Wizard's Hat
Try clearing out your mailbox.
That shouldn’t be the problem, I don’t have the “mail box full” tooltip achievement yet.
EDIT: Apparently it was because of that, even though I only had 4/10 messages on my mailbox. In fact it was keeping me from receiving mails from other players (and from gold sellers ready to be repported from now :P).
(edited by Lokheit.7943)