Returns the globally unique identifier (GUID) of the interface that defined the error.
IErrorInfo::GetGUID returns the GUID of the interface that defined the error. If the error was defined by the system, IErrorInfo::GetGUID returns GUID_NULL.
This GUID does not necessarily represent the source of the error. The source is the class or application that raised the error. Using the GUID, an application can handle errors in an interface, independent of the class that implements the interface.