[Erwin]

Open memberlist.php:

Find:

PHP Code:

if (!$enablememberlist) {
  eval("standarderror(\"".gettemplate("error_nomemberlist")."\");");
  exit;
} 


Replace with:

PHP Code:

if (!$enablememberlist or $bbuserinfo[usergroupid]!=5 or $bbuserinfo[usergroupid]!=6 or $bbuserinfo[usergroupid]!=7) {
  eval("standarderror(\"".gettemplate("error_nomemberlist")."\");");
  exit;
} 


Untested, but should work.