Cause: This happens when you try to create an HTTP ENDPOINT in SQL Server 2005 because the SQL Server process lacks permissions to register the endpoint with HTTP.SYS.
Fix: Issue the following command before executing the CREATE ENDPOINT
EXEC sp_reserve_http_namespace N'http://{hostname}:{port}/{path}'
In class today, we started off by talking about SQL Server 2005's Service Broker. Here's a few additional resources that I think help understanding Service Broker a bit easier:
If are looking for the inkboard drawing, here's a photo of it. I'll try to make it available as a Visio in the future.