Try WebRTC

Use htaccess file to redirect www to non-www domain.

Everything should work fine then.

See http://learn.elgg.org/en/2.0/appendix/faqs.html#login-token-mismatch

Temporarily ignore access control.

$ia = elgg_set_ignore_access(true);
// perform your operations here
elgg_set_ignore_access($ia);

Use this carefully!

As of Elgg 1.9 you can limit group content to members only, check the edit group page and find the setting "Accessibility of group content"

Where would you want to display it? If you don't care where then you can use Elgg's system message:

system_message('Message here.');

Hi, I want to show a persistent text with your own css, no modal... Thanks!

Use egg_list_entities() instead and you can get that specific blog's guid right from the url

blog/view/guid_here/

And you get something like this, I put the comments in the sidebar just for this example

Your code will fetch all the comments on the $gui_post entity. You have to iterate on those comments to output the data like,

$comments = elgg_get_entities(array(
                            'type' => 'object',
                            'subtype' => 'comment',
                            'container_guid' => $gui_post,
                         ));
if($comments){
    foreach($comments as $comment){
        echo $comment->description;
    }
}    

Or, like cim mentioned, you can use the elgg's listing view if you use elgg_list_entities() instead

echo elgg_list_entities(array(
                            'type' => 'object',
                            'subtype' => 'comment',
                            'container_guid' => $gui_post,
                         ));

Hi, I tested the code but not work, return null, the var $gui_post  equals '126' that is the guid of the article, I 'm doing something wrong ?.

$comments = elgg_list_entities(array(
                            'type' => 'object',
                            'subtype' => 'comment',
                            'container_guid' => '126',
                         ));

echo $comments;