the session test is failing.
when you click the first link on the session test page, it sets the session variable:
Session Test = test
when you click the second link, this should not change, but it does, it changes to:
Session Test = NULL
This means that the servers session management is not functioning. you will need to contact them to have the problem corrected.
Most likely, it is an issue with the session.save_path setting in the php.ini file, but the host will need to look into the issue to determine the cause.