Hello there and welcome to the Wowza support forum.
Are you testing playback with the Wowza provided Silverlight player? [install-dir]/examples/VideoOnDemandStreaming/SilverlightPlayer
Do you have the Silverlight plugin installed on the machine? And is it up to date?
Are you entering the correct URL for this player:
Does playback work with RTMP player?
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
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.
<!-- Properties defined here will override any properties defined in conf/HTTPStreamers.xml for any HTTPStreamer loaded by this applications -->
I hope this helps.