Installing and upgrading help

 I have installed the phpadmin module in the admin folder, but I must have done something wrong, because I get this message when I as admin activate the module.

No hostname (I have translated it from danish)
Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/amt/admin/mysql/libraries/common.lib.php:1124) in /var/www/html/amt/admin/mysql/index.php on line 42

Is there anyone who can help me.