Error when sending mail- emails not getting to all recipients

[gstuessy]

Hi, in mid-August I've seen a sharp drop in the # of people who are opening our e-newsletters, and wonder if the error below is related, what it means, and whether there's a solution? I'm not getting bounced emails, and the people I've checked with have said the messages aren't going into their spam; the emails aren't reaching some mailboxes at all. I tried to look at the source mentioned in the trace, but I couldn't figure out anything from it.

-----------------------------ERROR MESSAGE IN LOG-------------------------------------
Sep 17 13:56:26  [info] $Fatal Error Details = Array
(
    [message] => We can't load the requested web page. This page requires cookies to be enabled in your browser settings. Please check this setting and enable cookies (if they are not enabled). Then try again. If this error persists, contact the site adminstrator for assistance.<br /><br />Site Administrators: This error may indicate that users are accessing this page using a domain or URL other than the configured Base URL. EXAMPLE: Base URL is http://example.org, but some users are accessing the page via http://www.example.org or a domain alias like http://myotherexample.org.<br /><br />Error type: Could not find a valid session key.
   

Code: [Select]

=>
)

Sep 17 13:56:26  [info] $backTrace = #0 /home/afaeus/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Error.php(315): CRM_Core_Error::backtrace("backTrace", TRUE)
#1 /home/afaeus/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Controller.php(278): CRM_Core_Error::fatal("We can't load the requested web page. This page requires cookies to be enable...")
#2 /home/afaeus/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Controller.php(186): CRM_Core_Controller->key("CRM_Mailing_Controller_Send", TRUE, FALSE)
#3 /home/afaeus/public_html/wp-content/plugins/civicrm/civicrm/CRM/Mailing/Controller/Send.php(41): CRM_Core_Controller->__construct("New Mailing", "null", NULL, FALSE, TRUE)
#4 /home/afaeus/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(287): CRM_Mailing_Controller_Send->__construct("New Mailing", TRUE, "null", NULL, "false")
#5 /home/afaeus/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(70): CRM_Core_Invoke::runItem((Array:14))
#6 /home/afaeus/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(52): CRM_Core_Invoke::_invoke((Array:3))
#7 /home/afaeus/public_html/wp-content/plugins/civicrm/civicrm.php(344): CRM_Core_Invoke::invoke((Array:3))
#8 [internal function](): civicrm_wp_invoke("")
#9 /home/afaeus/public_html/wp-includes/plugin.php(505): call_user_func_array("civicrm_wp_invoke", (Array:1))
#10 /home/afaeus/public_html/wp-admin/admin.php(212): do_action("toplevel_page_CiviCRM")
#11 {main}