IISADMPWD Replacement Tool may deny access to the Admin page with a message similar to the following.

Server Error in ‘/’ Application.
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Access is denied.
Description: An error occurred while accessing the resources required to serve this request. The server may not be configured for access to the requested URL.

Error message 401.2.: Unauthorized: Logon failed due to server configuration. Verify that you have permission to view this directory or page based on the credentials you supplied and the authentication methods enabled on the Web server. Contact the Web server’s administrator for additional assistance.

This error often occurs if you do not have Windows authentication enabled for the IISADMPWD Replacement Tool web applications. Please check the IIS authentication configuration for each IISADMPWD Replacement Tool web application and ensure that both Anonymous and Windows authentication are enabled for both applications.

Note: You may need to install the Windows authentication role service. Check out https://support.webactivedirectory.com/portal/kb/articles/how-do-i-install-windows-authentication-in-iis-7-and-later for help installing this role service.