Method notesservicev1.exportNotes can not be reflected

We have consumed a third party web service and are trying to invoke it from an winform application. However when I instantiate the web service the following System.InvalidOperationException exception is thrown:

System.InvalidOperationException was unhandled

Method notesservicev1.exportNotes can not be reflected.

The XML element 'GetNotesInfoRequest' from namespace
'http://ift.tt/1QuWacL'
references a method and a type.
Change the method's message name using WebMethodAttribute or change the
type's root element using the XmlRootAttribute.

I got a link:

Method 'XYZ' cannot be reflected

But I am not getting what exactly I should do ?