Monday, 25 October 2010

The specified request cannot be executed from current Application Pool (403.18)

So you've split your apps into seperate app pools in IIS, which works well for app isolation on your web server and all is well until you start getting 403 HTTP status responses (with a substatus in the IIS logs of 18). This error is a result of your application running your application and the custom error page you've configured within different app pools.

The solution?

I'm afraid you're going to have to edit the registry!!! So back it up first then create a registry key with the name IgnoreAppPoolForCustomErrors, of type DWORD and value 1 under the HKLM\SYSTEM\CurrentControlSet\Services\W3SVC\Parameters\ folder.


  1. This comment has been removed by a blog administrator.

  2. Hi, after some research, I found that this can be caused by the fact that the application's physical path is a sub directory of a different application (e.g. the root application of a website).

    If you look at the applicationHost.config file and search for your site name, you will see that the root application contains a virtual directory entry (running under the parent application's app pool) as well as the sub application definition (running under a different app pool) and a virtual directory definition.

    I found that if I relocated the sub application's files to another physical location, thus removing the virtual directory entry from the root application, I no longer recieved this error.

    HTH :)