Process Monitor shows "path not found" for valid URLs

We use "Process Monitor" (ProcMon) to monitor the w3wc.exe process on a Windows Server 2008 running IIS7 . We have noticed that requests to perfectly legal urls still results in a "PATH NOT FOUND" entry in ProcMon.

For example, we have configured a handler in web.config like:

<add name="ImageVaultHandler.aspx_*" path="ImageVaultHandler.aspx" verb="*" type="ImageStoreNET.Classes.Handlers.ImageHandler, ImageStoreNET" preCondition="integratedMode,runtimeVersionv2.0">

Requests to this handler eg. "http://localhost/id_123/ImageVaultHandler.aspx" will return an image as expected, but when you analyze the request in ProcMon the w3wc.exe process looks to have unsuccessfully searched for a physical file with the same path in my web directory.

Is this behaviour by design? Or have we missed something, the application pool used is configured to run in "Integrated Mode".

This sounds reasonable to me - what IIS is probably doing is checking to see whether or not the file exists in order to determine what handler to use when processing that request:

It looks like the logic in IIS doesn't bother to check first whether there is an applicable handler that can be used even when the file doesn't exist.