Have you tried this one

http://sqlbuzz.wordpress.com/2011/12/07/connecting-to-the-integration-services-service-on-the-computer-mirrorstand-failed-with-the-following-error-access-is-denied/

Might be that 2008 R2 creates the MsDTSServer100 DCOM object and 2008 creates the MsDTSServer as I have both in my DCOM as I have both versions of SQL installed.