Andi, I did a new installation and i changed the user name:
I removed all commented lines here, but I kept on the files
[root@vcssweb01 conf]# more local.php
$conf['title'] = 'Wiki_Sales';
$conf['lang'] = 'en';
$conf['license'] = 'cc-by-sa';
$conf['useacl'] = 1;
$conf['superuser'] = 'wikiuser';
[root@vcssweb01 conf]# more users.auth.php
wikiuser:$1$DopXuvVd$CwD8pajNTxsRmSpHqXDEh0:Marcelo Resende:
marcelo.resende@email.com:admin,user