It's a SMF bug. It has something to do with special characters:
// Since the password got modified due to all the $_POST cleaning, lets undo it so we can get the correct password
$_POST['oldpasswrd'] = addslashes(un_htmlspecialchars(stripslashes($_POST['oldpasswrd'])));
Fixing this tangled mess of escaping would be difficult.
If your account email address works, do password recovery and change your password to something without special characters. If not, PM me and I'll change your email address.