The Add Web Reference dialog has no problem with the http://www.oakleaf.ws/cfr-soap/ cfrsearchws.wsdl file, which was created with the SOAP Toolkit 2.0. The ASP.NET/SOAP Toolkit version of the OakLeaf CFR XML Web services at http://www.oakleaf.ws/cfr-aspx/ default.aspx successfully creates a Web Reference from the WSDL and WSML files. (See Figure 12-2.) TIP Use the  ValidateWSDL  method of Microsofts WsdlVerify XML Web service at http://www.gotdotnet.com/ services/wsdl/wsdlverify.asmx to verify a WSDL file or document against the WSDL 1.1 specification. In some cases, the WSDL file passes Add Web Reference dialog muster, but the autogenerated client proxy returns SOAP errors when you execute it. The PHP-based newsgroup reader Web service at http://www.codecraze.com/soap/nntp.wsdl has an assortment of issues that prevent the Visual Studio .NET client proxy from generating an operable SOAP request message. C  h  a  p  t  e  r 1  2  : I  n  t  e  r  o  p  e  r  a  t  i  n  g w  i  t  h T  h  i  r  d  -  P  a  r  t  y W  e  b S  e  r  v  i  c  e  s 4 3 5 Figure 12-1 The Add Web Reference page wont accept this WSDL file, which was apparently created by an early version of the SOAP Toolkit.