This is likely your problem:

WARNING: "PHP session.use_trans_sid = ON"

How to resolve it?
You can try the following, and/or work with your hosting company for the best way to do it on "their" servers.
PHP Session.use_trans_sid should be disabled.

The session.use_trans_sid setting in your server's PHP.INI file is set to ON.

This could potentially cause you some problems with session handling and possibly even security concerns.

You can sometimes work around this by setting an .htaccess parameter such as described here: http://www.olate.com/articles/252, or you could disable it in your PHP.INI if you have access to it.

For more information on the security risks it imposes, see: http://shh.thathost.com/secadv/2003-05-11-php.txt.

(You may have to create the .htaccess file if you don't already have one.)