You may receive an "HTTP Error 401.5" error message when you open an ASP page that is hosted on Internet Information Services 6.0 (906474)

SYMPTOMS

When you browse to a Microsoft Active Server Pages (ASP) page that is hosted on a server that is running Microsoft Internet Information Services (IIS) 6.0, you may receive an error message that is similar to the following:

HTTP Error 401.5 - Unauthorized: Authorization failed by an ISAPI/CGI application. Internet Information Services (IIS)

However, when you open a static Web page on the same Web site, you may receive an error message that is similar to the following:

HTTP Error 401.3 - Unauthorized: Access is denied due to an ACL set on the requested resource. Internet Information Services (IIS)

CAUSE

This is a different behavior than in IIS 5.0. By default, the Verify that file exists option is not enabled in IIS 5.0. By default, the Verify that file exists option is enabled in IIS 6.0.

This issue occurs if the following conditions are true:

The Verify that file exists check box is selected in the Add/Edit Application Extension Mapping dialog box for the ASP Web application extension in IIS Manager.
You do not have the correct NTFS file system permissions in the discretionary access control list (DACL) to open the file.

RESOLUTION

To resolve this issue, set the appropriate NTFS file system permissions on the ASP file. For more information about how to set NTFS file system permissions in IIS 6.0, click the following article number to view the article in the Microsoft Knowledge Base:

812614 Default permissions and user rights for IIS 6.0

MORE INFORMATION

You receive the HTTP 401.5 error message because the access denied error occurs when the ASP ISAPI extension is verifying that the ASP page exists.