We are sending mouse events from a C# plugin to the rhino application. But we can not make rhino to drag objects when we send mouse down and subsequent mouse move events from our plugin. Everything else like selecting and deselecting works and it is visible that the cursor moves on the object so it is not likely about a mouse location problem. Here is how we are sending the mouse events to the application:
void sendMouseMessage(PureWebMouseEventArgs mouseEvent)
{
int X = (int)mouseEvent.X;
int Y = (int)mouseEvent.Y;
setClientViewMousePosition(X, Y);
IntPtr lParam = (IntPtr)((Y << 16) | X);
IntPtr wParam = IntPtr.Zero;
uint mouseEventType = convertMouseEventToInt(mouseEvent.EventType);
SendMessage(Rhino.RhinoDoc.ActiveDoc.Views.ActiveView.Handle, mouseEventType, wParam, lParam);
}