What happens if you enter the Manifest URL directly in a browser. It should return XML data.
You might add this property to http streamers in the Application.xml
<!-- Properties defined here will override any properties defined in conf/HTTPStreamers.xml for any HTTPStreamer loaded by this applications -->
This may fix the issue, the <Value>XXX</Value> can be tweaked up or down to suit your needs and is currently set to 10 seconds.