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When you use Group Policy to add multiple versions of an add-in as Office Outlook 2007 trusted add-ins, you may receive the following error message:
The name you entered has already been used. You need to enter a unique name.
To resolve this problem, apply the hotfix that is described in Microsoft Knowledge Base article 950282. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
950282 Description of the Office Outlook 2007 hotfix package: March 20, 2008
The inability to add two add-ins that have the same name for the GPO entry is a limitation of the Windows registry. This is because each .dll file name is stored as a registry key, and Windows does not let two registry keys have the same name. Therefore, you cannot use the same name for two add-ins.
The hotfix that is described in the "Resolution" section provides a solution to this problem by using the question mark character (?) as a delimiter. In Outlook 2007, any characters after the question mark are ignored and are not used in the add-in name. This behavior lets you use the characters after the question mark as a comment to help document the add-in. For example, consider the following scenario:
You have three add-ins that all have the same file name, and this name is "myaddin.dll."
The first .dll file name of the add-in is used for a Workflow project. The second .dll file name is version 1.0 of a department add-in, and the third .dll file name is version 2.0 of that department add-in.
To create a GPO to trust all three add-ins in this scenario, you can use the following three names:
Addin.dll?WorkFlow Project Add-in
Addin.dll?Version 1.0 of Department Add-in
Addin.dll?Version 2.0 of Department Add-in
Therefore, when Outlook 2007 reads the add-in names, all the text after the question mark, together with the question mark, is ignored. This behavior lets multiple, different add-ins successfully use the same name.