[qmailadmin] Qmailadmin return =?iso-8859-1?Q?=22Error:?= Illegal =?iso-8859-1?Q?username=22?= when changing password

[[EMAIL PROTECTED]]

Hi, i've my server with Qmail+Vpopmail+Qmailadmin, all works fine, but when 
i try to change the password of a vpopmail user via Qmailadmin, i receive 
the error:
Error: Illegal username