On the Edit menu, point to New, and then click DWORD Value.
Type EnableLocalMachineVSTO, and then press ENTER.
Right-click EnableLocalMachineVSTO, and then click Modify.
In the Value data box, type 1, and then click OK.
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:
929590 Known issues when you develop custom solutions for Office Outlook 2007
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.