AI OnAI Off
I know I'm late to the party but what you probably want to do is enabling Load User Profile in the Application Pool for your web app, this is default set to false to emulate IIS 6 behaviour.
Props: http://geekswithblogs.net/ProjectLawson/archive/2009/05/05/iis-system.web.aspnethostingpermission-exception-on-windows-7-rc.aspx
See also http://world.episerver.com/Blogs/Johan-Bjornfot/Dates1/2010/1/Workflow-image-generation-failure/
any one have seen this error Access to the regisry key 'HKEY_CURRENT_USER\software\microsoft corporation\internet information services\7.5.7600.16365' is denied when call the view workflow image.