The HttpWorkerRequest documentation states:
... your code could create a derived class for the purpose of child-request execution within a given application in order to pass its instance to ProcessRequest. In this case, the derived class should keep a reference to the current HttpWorkerRequest and delegate most of the methods to it.
That works fine in Classic Pipeline Mode under IIS7. However, in Integrated Pipeline Mode the child request silently fails.
In July I discussed this issue on forums.iis.net with Mike Volodarsky, a Program Manager on the IIS team. He acknowleged the issue and at the end of the thread said he would look into whether restoring the ProcessRequest functionality was feasible, but I haven't heard back. The thread is at: