See this blog post for more information on what this solution does:

http://blogs.technet.com/b/servicemanager/archive/2011/05/03/cancelling-pending-activities-when-a-change-request-fails.aspx

To deploy:

  1. Install SMLets Beta 3 (or newer) on the SCSM management server.
  2. Import the MP .xml file.
  3. Copy the .dll file to C:\Program Files\Microsoft System Center\Service Manager 2010 directory (or whatever directory you have installed into) on the SCSM management server that is running the workflows.