Because data of a LabVIEW class is private, you can bundle or unbundle only wires of LabVIEW class types in VIs that are members of that class. This VI is not a member of the LabVIEW class.
To correct this error, you can add this VI to the class, which gives this VI permission to access the data. Alternatively, you can replace the Bundle or Unbundle functions with subVI calls to VIs that are already members of the class that might return the value you were attempting to access. If a developer created a subVI for the class, you can find the subVI under the class in the Project Explorer window.