A 2007 Office system application does not load an add-in that is developed by using VSTO

A 2007 Office system application does not load an add-in that is developed by using Visual Studio Tools for Office (VSTO).

Note VSTO add-ins are registered under the HKEY_LOCAL_MACHINE key.

To resolve this issue, apply hotfix package 976477, and then enable the hotfix package. To do this, follow these steps:

1. Apply hotfix package 976477. For more information about the hotfix, click the following article number to view the article in the Microsoft Knowledge Base:
   976477  (http://support.microsoft.com/kb/976477/ ) Description of the 2007 Office system hotfix package (Mso-x-none.msp): October 27, 2009
2. Enable the hotfix package. To do this, follow these steps:
   1. In Windows Vista, Click Start
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      , type regedit in the Start Search box, and then press ENTER.
      
      
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      If you are prompted for an administrator password, type the password. If you are prompted for confirmation, provide confirmation.
      
      In Windows XP, click Start, click Run, type regedit in the Open box, and then click OK.
   2. Locate and then click the following registry subkey:
      
      
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\12.0\Common\General\
   3. On the Edit menu, point to New, and then click DWORD Value.
   4. Type EnableLocalMachineVSTO, and then press ENTER.
   5. Right-click EnableLocalMachineVSTO, and then click Modify.
   6. In the Value data box, type 1, and then click OK.
   7. Exit Registry Editor.

By default, VSTO-based add-ins are displayed in the COM Add-ins window. You have the option of hiding these add-ins in the COM Add-ins window by deploying the DontDisplayHKLMAddins registry entry.

For more information about the DontDisplayHKLMAddins registry entry, click the following article number to view the article in the Microsoft Knowledge Base: When you deploy both the EnableLocalMachineVSTO and DontDisplayHKLMAddins registry entries, the add-ins are listed in the Trust Center of a 2007 Office system. Additionally, you cannot remove the add-ins because they do not appear in the COM Add-ins window.

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