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After you install Cumulative Update 1 (CU1) for Microsoft BizTalk Server 2013 R2, the Minimal Lower Layer Protocol (MLLP) adapter 2-way send ports do not suspend if they time out while waiting on the downstream system to return an acknowledgement. Instead, the send port instance completes without publishing back any response message.

Orchestration instances waiting for a response message or an exception will remain dehydrated. Even if Order Delivery is turned on, the send port may continue to send subsequent messages instead of queuing all messages while waiting for the ACK.

This issue occurs when one of the standard set of ACK codes is selected from the Acceptable ACK Codes property.

Additionally, you may receive the following error message:

MLLP Send adapter timed out while receiving the ACK.


This issue occurs after CU1 for BizTalk Server 2013 R2 is installed. CU1 adds support for handling custom ACK codes, and it unintentionally changes the behavior for handling standard ACK codes if a timely ACK is not received from the downstream system.


Cumulative update information

For BizTalk Server 2013 R2

The fix that resolves this issue is included in Cumulative Update 5 for BizTalk Server 2013 R2.

Note The fix restores the correct behavior for standard ACK codes to be consistent with the release version of BizTalk Server 2013 R2.


To work around this issue, select CUSTOM and then type the ACK codes in the textbox. For example, type AA, CA, AE, CE instead of selecting AA, CA, AE and CEĀ from the dropdown menu.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.


Learn about service pack and cumulative update list for BizTalk Server.

Learn about BizTalk Server hotfixes and cumulative update support.

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