A SOAP fault is an error in a SOAP (Simple Object Access Protocol) communication resulting from incorrect message format, header-processing problems, or incompatibility between applications.
When a SOAP fault occurs, a special message is generated that contains data indicating where the error originated and what caused it. This data is called a fault element. A message that includes a fault element is known as a fault message. A fault message can be generated by any node , and is transmitted to the first upstream node (the node immediately preceding it in the message path).
SOAP allows computer programs to communicate over a network even if they use different operating platforms. It employs the World Wide Web's HTTP (Hypertext Transfer Protocol)and XML (Extensible Markup Language) as the mechanisms for information exchange.