The underlying connection was closed: The connection was closed unexpectedly.

I’m sure there are numerous reasons for this error, but here’s one I encountered today.

First the background. We have BizTalk server connecting to an internal Open/AS2 server running on Linux. That Linux server was re-installed on a Virtual Machine; and I had agreed with the Linux guy to change the AS2-ID (defined in the Trading Parties) from BiztalkTest to BizTalkProd. However, he didn’t make the change on his side.

So when he looked at the logs, he could see that it was receiving data, but as he described it “the server didn’t know what to do with it.” That means, it didn’t generate the MDN and send it back to BizTalk.

I had defined my SendPort was a two-way (Static Solicit-Reponse) and was using content-based routing. So we sent the message to the AS2 server, and didn’t get a response back, giving the “underlying connection closed unexpectedly” error.