Hi Shubham,

This error happens when the chief ray can not make it to the image plane, so you need to figure out why the chief ray is being blocked in your system (TIR? Apertures?) and if there is a way to unblock the chief ray and let it propagate through to the image plane so you can view the Spot Diagram. 

The best tool to check the chief ray path and understand why it's being blocked and at which surface, is the Single Ray Trace (Analyze > Rays & Spots). This tool lists the ray intercept coordinate surface by surface and will tell you if the ray is being vignetted at a surface. So you can define the chief ray (the ray that travels from a specific field point, through the center of the entrance pupil, and on to the image surface) and check what it's happening.

The Analyze Tab (sequential ui mode) > Image Quality Group > Rays and Spots > Single Ray Trace

Best,

Berta

Berta is right, you should find out why the chief ray is not making it through. For wavefront analyses, this is fatal: the reference sphere is chief ray referenced, so no chief ray means no reference sphere.

For rays, spot diagrams and analysis with 'Geometric' in the title, it's not fatal. In the Spot Diagram, change 'Refer to' to Centroid

But if you can, fix the chief ray trace problem. No chief ray means no first-order (paraxial) properties for the lens.