The core of Biztalk is the messagebox, receive ports and orchestrations publish messages into the messagebox and send ports and orchestrations subscribe to messages from the messagebox.
If you publish a message to the messagebox with no enlisted subscriber then you will get this error.
You can view the active subscriptions using the Biztalk admin console:
[url]http://geekswithblogs.net/sthomas/archive/2005/10/03/55872.aspx[/url]
A subscription is basically a filter on promoted context properties.
For straight thru processing you declare a receive port and a send port. The send port will have the a filter of BTS.ReceivePortName = [i:dc6d4ac4c9]receive port name[/i:dc6d4ac4c9]. So it will subscribe to all messages coming from the named receive port.
A send port without a filter has no subscription – although if bound to an orchestration the subscription is created when the orchestration is enlisted.
Check your message context properties and see if they match any of the subscriptions