Error using "Send Product Catalog" feature of Navision 4

Goal: send a Navision Product Catalog to BizTalk 2006.

In Navision “Partner Setup”, I have configured a BizTalk partner. For this partner, I have the “Destination Address” set to http://localhost/CommerceGateway40/BTSHTTPReceive.dll. I have Commerce Gateway (and BizTalk server) installed locally. “Export Product Catalog” is active as an agreement type.

In Navision, when I select “Purchase/Inventory & Costing/BizTalk Product Catalogs/Send Product Catalog”, and accept the defaults, I receive the following Navision alert dialog: “An unknown error has occurred”. The following error is in the application log:

Source: Navision TCP Class; Description: Root element is missing.

I am using the CRONUS USA, Inc. sample database.

Can anyone help?