Fix “The add-in could not be installed or loaded” Outlook error message

Unfortunately, for IT Administrators, there are many third-party programs out there that install add-ins to Microsoft Outlook. This is sometimes very useful, such as better search programs like Google Desktop or Windows Desktop Search, but it’s also very annoying, like when Adobe tries to add PDF buttons to the entire Office suite!

Eventually, when you go to uninstall a program or update it, sometimes you end up getting the following error message when you open Outlook:

The add-in “abc” could not be installed or loaded.


The add-in Symantec Antivirus 10.1 cannot be loaded and has been disabled by Outlook

It may also be followed by something to the effect of “You may be out of memory, out of system resources, or missing a .DLL file”.

Sometimes Outlook will simply close, other times you can continue working, but have to keep seeing that error over and over again. Whatever the case may be, something has become corrupted in Outlook and that’s why you are getting the error.

There are a few different ways you can try to solve the problem and I’ll go through the methods that I know of.

Method 1 – Use Detect and Repair

The quick and easy way to try and fix this issue is to run Detect and Repair from the Help menu. If you are running Outlook XP or Outlook 2003, you will find Detect and Repair under the Help menu. If Outlook 2007, it is now called Office Diagnostics.

office diagnostics

It will run through a list of diagnostic checks and automatically fix any errors that it finds with Outlook.

detect and repair


Method 2 – Rename Extend.dat file

The Extend.dat file is what is used by Outlook to cache registry entries of third-party add-ins. If you delete this file, it will disable all of the add-ins and re-create the file.

To rename the file, click on Start, then Search. Make sure to choose All files and folders and then type in Extend.dat and search your entire local hard drive.

extend dat

Also, be sure to check the boxes under Advanced Options for searching system folder and searching hidden files and folders. Only one entry should come up and it should be located in your user profile under Documents and Settings.

Rename it to Extend.old and restart Outlook. The file will be recreated and hopefully will not be looking for the add-in from the uninstalled program anymore.

Hopefully one of these two methods solved your problem! If not, post a comment and I’ll try to help you out. Enjoy!

Comments [3]

  1. Hi,

    Thanks I have tried your both solutions . But none of them is not working . Actually in our case we have devloped our own custom dll which we are loding at the time of outlook startup.

    It was working fine earlier but now on the outlook startup it is prompting that may be dll is not loaded and installed.

    Please help me out because when I am trying to add Add-in(dll) through (Tools-others tab-advanced -com add-in manager ) it is prompting that this is not valid dll.

  2. It worked for me – thanks a lot for your help.

  3. I hope my experience can help others in a similar situation.

    I recently migrated from XP to Windows 7 and reinstalled Outlook 2003 and other software I considered a must namely Symantec antivirus SEP v11 and Google Desktop v5.9 (I know, it is no longer supported by Google but I did not find any decent close alternative yet to index fileystem and Lotus Notes DBs: long life to GD !).

    When Outlook started it complained about missing add-in dll for vpmsece.dll (Symantec) and GoogleDesktopOffice.dll)

    I noticed it was looking for it under the 64-bit directory “Program Files” and not where they actually ended up after migration, that is “Program Files (x86)”.
    So I simply copied both of them under “Program Files” , manually creating the needed folders and … voila: it worked: no more complains and both applications doing their job on Outlook mails (namely: AV scanning and mail content indexing).

    Then I read your post and I gave it a try, temporarily renaming my copied .DLLs and extend.dat and allowing Outlook to recreate one. No success: I mean it stopped complaining but also the application were no longer working on e-mails.

    bottom line: if you want to get rid only of symptoms because the original apps are no longer there then recreation of extend.dat works. Otherwise it is like curing the symptoms and not what they represent.

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