Access Denied while validate Workflow URL ?

When i am trying to validate the URL http://MDT579:81/MicrosoftDynamicsAXWorkflow50 in Workflow Infrastructure Configuration Wizard i am getting the following error

Server was unable to process request. —> Access is denied

I am to able to browse the Workflow Directory Page and i’d already given full permission to bcproxy account (the dedicated account through which Workflow was installed successfully)on workflow folder.

try to validate again and it will dissapear!! what a magic

Give the identity of bcproxy user in the Application pool used in the workflow