Error message: “The Web site http://server/sites/site_name was not created correctly. Exception: No .NET Business Connector session could be found.”

This is because of  Business Connector configuration.
So it might not be configured correctly. To verify the configuration, follow this procedure:

1. On the server that runs IIS and hosts your Enterprise Portal site, click Start > Administrative Tools > Microsoft Dynamics AX Configuration Utility.
2. In the Configuration target list, click Business Connector (non-interactive use only).
3. On the Connection tab, verify the server name and the TCP/IP port. If the port is blank, it is assumed to be running on port 2712. To verify the actual port on the AOS server, view Dynamics Information events in the Application Event log after the AOS has started.
4. If necessary, update the configuration or create a new configuration (click Manage > Create configuration).