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I'm mapping new file types in IIS 6 to the ASP.NET processor; for example the .gif image type.

IIS will see a GIF image doesn't not exist (e.g. ) and raise a 404 HTTP err before passing the request onto ASP.NET. I want to turn off the IIS file check so ASP.NET gets to handle the invalid request how it chooses.

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up vote 0 down vote accepted

Look at the setting "verify that file exists" in the extension or ISAPI mapping handling that extension. If that option is enabled, IIS will see that the file doesn't exist and handle the 404 itself before ASP is ever called. If the setting is not enabled, IIS will pass the request to ASP and let the filter handle it internally.

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