OL2007, VS2008, C#, VSTO

My form region is not appearing on machines I deploy to even though it
appears fine on the development machine.

http://msdn.microsoft.com/en-us/libr...aspx#Deploying says:

Deploying a Form Region
Form regions are deployed automatically with the associated Outlook add-in.
Therefore, you do not have to perform any special tasks to deploy a form
region. For more information about deploying add-ins, see Deploying Office
Solutions (2007 System).

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Any ideas why it wouldn't be showing up? I've tried on a Vista and an XP
machine.