The Web Services Description Language tool (Wsdl.exe) generates proxy code for XML Web services. The generated types that are used in the proxy class are based on the contents of the WSDL document that describes the XML Web service. However, the generated types might not be what you want nor what you expect.
Wsdl.exe determines the best generated type to use for the objects that are specified in the service description. In some cases, the tool uses a least-common-denominator approach for casting objects to a type. For example, an ArrayList parameter in a WebMethod is described in WSDL as a XML Schema (XSD) sequence. When Wsdl.exe finds this array description in the service description, Wsdl.exe then generates a proxy class that uses an Object Array. You may prefer to work with an ArrayList, which was the original type that was used in the WebMethod. If you do not want to use the generated types, you can change the generated types to more desirable types. To get the appropriate object type, you can open the file that contains the generated proxy class, manually change the generated method parameter, and then return types to the appropriate object types.
XML Web services serialize objects to XML and then deserialize the XML back to objects. Generally, an object of a particular type can be serialized and then deserialized to another object of the same type. However, if you use different types, this may not work.