I have 3 images (618, 619, 620). I have measured the fiducials and provided the interior orientation for each image that makes up the block. The Exterior orientation is not known. So, I need to determine the control points and I'm ready for the tie points. When I do all the necessary regulations and click on the RUN button, an error message appears "Exterior orientation estimation can not be solved with c:/aerial/dram619.img!". I don't know what this means and I can not find out what I have done wrong. Can you help me?