The line I think you're referring to in the admin.php reads
echo "<a href='".XOOPS_URL."/modules/system/admin.php?fct=".$file."'><strong>" .trim($modversion['name'])."</strong></a>\n";
But this line is the same in the installation that works and the one that doesn't.
I checked registered users and they have access to everything, but I didn't get that far anyway. Theme etc the same, just left it at default. Played with the banner on the one that doesn't work afterwards while waiting for an answer.
As it seems knowone has ever had this problem I can only guess that it's something very specific to the server it's on. I'll have to move eveything to another server or find a CMS that works.
Thanks