I'm having a problem that is killing me for two days.
The problem is that I have to configure two reports (ColdFusion+DotNet) on IIS (Server 2008, V7.5) such that they work on seperate application pool. But if I configure such in such that way I get an error

"HTTP Error 403.18 - Forbidden

The specified request cannot be processed in the application pool that is configured for this resource on the Web server".

But this is solved if I put the application on the same pool as default website,but then the second application and the first would be on the same app pool.

I also noticed that this problem doesn't occur on windows server 2003 IIS.

I also tried isolating my application away from inetpub,that din work too

Why is this happening?


This occurs when an application uses custom error pages hosted within an application in another application pool.

As you've discovered you can work around it by putting the two applications in the same application pool, or you can instruct IIS to ignore app pool boundaries when executing requests that result in custom errors. Navigate to the following key in the registry:


Create a new DWORD with name "IgnoreAppPoolForCustomErrors" and value 1

You'll need to issue an IISRESET /restart command from an elevated command prompt to active this change.

  • Hi,Im still having the same problem,any other ideas?? – Selv Oct 4 '13 at 7:31
  • If the server is not publicly accessible, switch to detailed error pages for the application that fails – Mathias R. Jessen Oct 4 '13 at 8:01
  • I've switched to detail error pages but din work.. – Selv Oct 4 '13 at 8:37
  • Selv: Did you ever figure this out. I'm having the exact same situation as you with ColdFusion 10 and IIS 7.5. If I run them under the same app pool, I do not get that error but I don't want to do that. – Brad Sep 12 '14 at 15:02

Do you have URL Rewriting in play? I've seen that error occur when a URL is rewritten by the Default Web Site (running in DefaultAppPool) to an application URL (running in a different app pool) in IIS 7.5.

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