Unable to open the ASMX page from the Sharepoint 'Vti_bin' folder in the IIS server. Getting following error "HTTP Error 401.1 - Unauthorized: Access is denied due to invalid credentials." in Internet Information Services (IIS).

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Reason for failure

=> ".asmx" login validation was disabled in the "web.config" file. That's a reason we are unable to open the ".Asmx" file from the IIS server.

path="*.asmx" validate="false"

=> Please check this entry for the non-working sharepoint site.

<add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />

<add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />

<add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" validate="false" />

remove verb="*" path="*.asmx" /> .

=> I was able to resolve the error by removing the following entry from the non working sharepoint site web.config file.

=> <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />

<remove verb="*" path="*.asmx" /> "" <==

NOTE: In default 'web.config' file you will not see above code. My customer has installed some third party custom workflow software due to that entry was added in the 'Web.config' file.