There are a few types of errors you may receive.
•Permission Denied errors will result if the user ID provided during authentication doesn't have sufficient access rights to perform the requested functions.
•Client-side errors. For example, an error would result if you tried to create a record but didn't populate one of its required fields.
•Server-side errors. After you generate client-side source code from the WSDL files, the WebServiceFaultDetail class provides a property, detailedErrorMessage, that is a wrapper for server-side error messages.
For server-side errors, the server throws the error, which is wrapped in an .XML message. This message is returned to the client and translated to a .JAVA object (or the appropriate programming language object equivalent) with the exception.