I was recently working on an HL7 solution in which I encountered the below error message. I was trying to send an HL7 message using MLLPSender tool and while receiving this message from an MLLP BizTalk receive location,
I got the below error message. 

Log Name:      Application
Source:        BizTalk Server
Date:          5/6/2013 2:14:35 AM
Event ID:      5815
Task Category: BizTalk Server
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      BTS2013.domain.name.domain.com
A response message sent to adapter "MLLP" on receive port "ReceivePort4" with URI "localhost:21000" is suspended.
 Error details: There was a failure executing the response(send) pipeline: "BTAHL72XPipelines.BTAHL72XSendPipeline, BTAHL72XPipelines, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35" Source: "BTAHL7 2.X Assembler" Receive Port: "ReceivePort4" URI: "localhost:21000" Reason: Message had parse errors, can not be serialized 
 MessageId:  {EBD75918-EEB0-4C24-9EBE-725D3DD7BA88}
 InstanceID: {CD369804-E9AD-4C32-8F2C-1541682BCBBF}

At the first sight, you may think that the message I am sending is wrongly formed and is not a correct HL7 message. I did several checks on my message and it looked good. After doing a bit of research and troubleshooting, I came to know that the problem was with the party configuration that I had in the “BTAHL7 Configuration Explorer”.

I noticed that schema namespace under the validation tab in the party configuration was incorrect and hence BizTalk was not able to validate my message correctly.
For some reasons, it got changed to http://microsoft.com/HealthCare/HL7/2X12.

I corrected the target namespace and did one more test after a host restart. Everything started working now. Although, it was a very small issue, it ate a lot of my time. I hope this helps you guys in your HL7 adventure.
Instead, it should be http://microsoft.com/HealthCare/HL7/2X

Written by
Yakshit Gohel

Reviewed by
Jainath V R 

Microsoft India GTSC