GUID's attached to structs have to be the same across multiple declarations and definitions of the same struct. So the following example would cause this error:

class __declspec(uuid("19a76fe0-7494-11d0-8816-00a0c903b83c")) foo;

class __declspec(uuid("00000000-7494-11d0-8816-00a0c903b83c")) foo{}