HTTP请求未经授权，客户端身份验证方案为“匿名”。从服务器收到的身份验证标头是'NTLM'

I have an ASP.NET web application written in VB.NET. One part of the application makes an AJAX call to an internal ASMX file which in turn makes a call to a remote web service which is just a single ASMX file. Normally this works fine and has been deployed a couple of times and works fine. One client however, is getting the message from the AJAX call: I have an ASP.NET web application written in VB