Login Problems with ID instead Nickname

Hello,

we are using smart commnity 6.1.6

A view people said they cannot login, so i test it and can login.

So i try to find out what is different.

If i login on http://www.nordsee-suche.de/portal/member.php

i can login with ID an Password or Nickname and Password.

If i Login via popup Menu Like this:

<a href="http://www.nordsee-suche.de/portal/member.php" onclick="showItemEditForm('login_div'); $( '#login_div' ).show().load( 'http://www.nordsee-suche.de/portal/member.php?action=show_login_form&amp;relocate=' + encodeURIComponent( '/portal/member.php' )  );return false;">Anbieterlogin</a>

(in the right upper corner)

So i can only login with NickName and Password but noth with ID and Password,

Have anyone a idea?

Thanks Jahn