Hello John
I think we can find together the solution to this problem.
We use a Joomla extension called JMS Multisite. Talking on the developer forum about redirecting
/plugins/system/screenreader/screenreader/libraries/tts/proxy.php
for
/plugins/system/screenreader/screenreader/libraries/tts/installation/index.php
and I had the following response:

"The behavior you describe with the que URL ending with /installation/index.php
/plugins/system/screenreader/screenreader/libraries/tts/installation/index.php
is the symptom of a developer who Performed the Joomala 1.5 initialization rather que Joomla 2.5 initialization.
This is probably because the "proxy.php" is an ajax or similar file que initialize the joomla an independent application.
Under the Joomla 1.5 intilisation que can be foundin in the "index.php" is The Following
define ('_JEXEC', 1);
define ('JPATH_BASE', dirname (__ FILE__));
define ('DS', DIRECTORY_SEPARATOR);
require_once (JPATH_BASE .DS.'includes'.DS.'defines.php ';
require_once (JPATH_BASE .DS.'includes'.DS.'framework.php ';
In Joomla 2.5 (or higher), as you can see in the index.php, the initialization is different
define ('_ JEXEC', 1);
if (file_exists (__ DIR__. '/defines.php')
{
include_once __DIR__. '/defines.php';
}
if (! defined ('_ JDEFINES')
{
define ('JPATH_BASE' __DIR__);
require_once JPATH_BASE. '/includes/defines.php';
}
require_once JPATH_BASE. '/includes/framework.php';
The problem is due to collegues developer did not tested if the "defines.php" is present in the root directory.
JMS used this feature present in Joomla 2.5 or higher to get the hand on joomla before its initialization and add the multisite functionalities.
So ask to the author of the "proxy.php" to perform the correct Joomla 2.5 initialization. "
Thanks for listening.