I'm using the JEDI .NET support to call methods on a class from a .NET assembly, using the method outlined in the part after "Update", here: https://stackoverflow.com/a/2052196/3164070 Except that I'm receiving the error: EOleException with message 'Method 'MTData.Transport.Tracking.TrackingAPI.SendDriverMessage' not found' Using ILSpy I can see that the method is public, and I am able to call other methods on the same class. I note that the method has a "default" parameter, and I'm wondering whether that's causing the problem. ILSpy shows the method as: public DriverMessage SendDriverMessage(int fleetId, int vehicleId, string message, string messageRef, bool replyRequired, string name, string location, string phoneNumber, double latitude, double longitude, DateTime? expiryDate = default(DateTime?)) Any clues as to how to resolve this? Note that the supplier of the assembly is unwilling to modify their assemblies to strongly name them...