Error: 'The add-in .. 'CmdExtN/CmdExtNP.dll' could not be installed or loaded'

Topic T1065 Applies to All NEO products


When starting NEO or Outlook you receive an error similar to the following:

'The add-in "C:\Program Files\NEO\CmdExtN.dll" could not be installed or loaded. This problem may be resolved by using Detect and Repair on the Help menu.'

This problem is caused by a file named EXTEND.DAT which is an internal cache file used by Outlook to store paths to all DLL files used for Outlook extensions. This is an Outlook defect wherein the cache is not properly refreshed by Outlook when command extensions are added or removed in the registry (typically during an uninstallation). The problem is made worse by the fact that Outlook error message recommends a Detect and Repair operation which does not fix the problem.


There are two methods to resolve this problem. If Method A does not work for you, try Method B.

Note that performing a Detect and Repair operation as per the Outlook error message does not solve the problem.

Method A

  1. Start Outlook.
  2. For Outlook 2003 navigate to 'Tools | Options | Other tab | Advanced Options button | Add-In Manager button'
    For Outlook 2007 or later navigate to 'Tools | Trust Center', select Add-ins and select Manage 'Exchange Extension' from the pulldown menu at the bottom of this page
  3. Depending on the NEO product you just uninstalled, uncheck the appropriate entry in the list.

Method B (extracted from Microsoft Knowledgebase Article identified below)

If you still receive the error message when you restart Outlook, refresh the Extend.dat file. Follow these steps:
  1. Quit all programs.
  2. Click Start, choose Find and click Files or Folders.
  3. In the Named box, type extend.dat.
  4. In the Look In list, click to select your hard drive.
  5. Click to select Include subfolders and click Find Now.
  6. In the Name list, right-click on the file Extend.dat, and on the shortcut menu click Rename to rename the file to Extend.old.
  7. On the File menu, click Close to exit.
  8. Restart Outlook. Restarting Outlook creates a new Extend.dat file.

For more information, see Microsoft Knowledgebase Article:;en-us;204951

Last updated: 16 May 2010