When you use the Microsoft BizTalk Server Accelerator for HL7 to process HL7 messages, an error message that resembles the following may be logged in the Application log:When this problem occurs, the TwoWayAckReceivePort receive port does not receive acknowledgement messages as expected.

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This problem can occur if the following conditions are true:

•	You configure the Minimal Lower Layer Protocol (MLLP) adapter receive handler and the MLLP adapter send handler to use different host names.
•	You use a solicit-response send port to send HL7 messages.

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To work around this problem, follow these steps:

1.	In the BizTalk Server 2006 Administration Console, create a dedicated host.
2.	Create a host instance. Configure this host instance to use the host that you created in step 1.
3.	Create a receive handler and a send handler for the MLLP adapter. Configure the receive handler and the send handler to use the host that you created in step 1.
4.	Configure the TwoWayAckReceivePort receive port to use the receive handler that you created in step 3.
5.	Configure the solicit-response send port to use the send handler that you created in step 3.
6.	Restart the BizTalk Server host.

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The BizTalk Accelerator for HL7 uses a special one-way MLLP receive port to receive acknowledgement messages on a one-way send port. The BizTalk Server Accelerator for HL7 Setup process creates the TwoWayAckReceivePort receive port to receive acknowledgement messages. The TwoWayAckReceivePort receive port is configured to use the TwoWayAckReceiveLocation receive location.

When you configure the send port to use the solicit-response mode, the receive handler for the TwoWayAckReceiveLocation receive location and the send handler for the send port must be configured to use the same host. This configuration is required for BizTalk Server to process acknowledgement messages correctly. For example, when you install the BizTalk Server Accelerator for HL7, the TwoWayAckReceiveLocation receive location is configured to use the BizTalkServerApplication host. Therefore, you must configure the send port to use the BizTalkServerApplication host as the send handler.

When the receive handler and the send handler for the MLLP adapter are configured to use the same BizTalk Server host, the TwoWayAckReceivePort receive port receives acknowledgement messages as expected.

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