Duplicate emails are sent unexpectedly from servers that contain the Async Service for Microsoft Dynamics CRM 4.0

Consider the following scenario. You install multiple platform servers that contain the Async Service for Microsoft Dynamics CRM 4.0. The servers have the Read Committed Snapshot Isolation (RCSI) feature enabled. When you perform a Bulk Email operation in this scenario, you notice that duplicate emails are sent unexpectedly from each server running the Async Service.

*Though title and symptoms here describes particular issue as Bulk Email operation, any Asynchronous Jobs, like Data Import, are also subjects to be affected by this.

This problem is fixed in the latest cumulative update rollup for Microsoft Dynamics CRM 4.0.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Note This problem was originally fixed in Update Rollup 12 for Microsoft Dynamics CRM 4.0.
For more information, click the following article number to view the article in the Microsoft Knowledge Base: Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 (https://vkbexternal.partners.extranet.microsoft.com/VKBWebService/ViewContent.aspx?scid=kb;en-US;322756&PortalId=1) How to back up and restore the registry in Windows

To enable this hotfix on the computer that is running Microsoft Dynamics CRM 4.0, follow these steps:

1. Under the
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSCRM
   registry subkey on the Microsoft Dynamics CRM server, add the following DWORD registry entry:
   AsyncDBAppLock
2. Set the value of the registry entry that you just added to 1.
3. Restart the Async service.

You can also work around the issue if you use one of the following methods:

• Disable the Async Service on all servers except one.
• Disable the Read Committed Snapshot Isolation (RCSI) feature.

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

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: For more information about Microsoft Business Solutions CRM software hotfix and update package terminology, click the following article number to view the article in the Microsoft Knowledge Base: