When configuring IIS 7.5 and the jakarta ajp redirector to Jboss, IIS attempts to download the isapi_redirect.dll instead of executing it and displaying the immanage page or the IDM user console.
The execute permission needs to be enabled within IIS. On the virtual directory you created in IIS for the isapi_redirect.dll,
* Open the Handler Mappings
* Click Edit Feature Permissions
* Check the box for Execute and click OK.
For further assistance please contact your IIS adminstrator or Microsoft Support.
Try a Google search for:
iis 7.5 dll downloads instead running
enable isapi-dll handler mapping
This is also a good link with full instructions for configuring the ISAPI_REDIRECT.DLL in IIS: