Microsoft KB Archive/175402

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XCLN: An Extension Failed To Initialize

Article ID: 175402

Article Last Modified on 10/28/2006


  • Microsoft Exchange Client 5.0
  • Microsoft Exchange Client 5.0

This article was previously published under Q175402

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.


When you attempt to start the Microsoft Exchange Client, you may receive the following error message:

An extension failed to initialize. The entry point could not be


The name or path of the DLL where the custom command resides is incorrect. This entry can optionally be followed by a comma and the ordinal of the entry point to call (default is 1).


Using the Registry Editor, ensure that the path statement in the dialog box correctly points to the DLL in question and that the original is correct. In the CleanSweep utility (Clnsp32.dll) located in the Back Office Resource Kit the ordinal is 2.

Example: Winnt4.0; c:\windows\system32\clnswp32.dll;2

This is assuming your OS is installed in C:\Windows and the DLL is in the System32 subdirectory.

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

To repair the problem, perform the following steps:

  1. At the command prompt, type RegEdit.
  2. In the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\Client \Extensions registry key, add the following New String value: Clnswp
  3. Note that the Data value for this String value should be as follows:


if you copied Clnswp32.dll to the proper directory (c:\Windows\System32) when installing the tool.

Additional query words: cleansweep clnswp xcln

Keywords: kbprb KB175402