Hi @Photoniker,

This is a challenging question to answer without more information about your design. Is there a file (or example file with this issue) that you can share here?

Could you describe more details about what specific components or parameters you were working on when it crashed?

Best,
Ethan 

Unfortuantly, I can not share a file or have a minimal example. It is a NSC model with user-defined dlls as well as CAD object. However, why should that be depended on the object. I have used the latest version of OpticStudio. 

Hi @Photoniker,

It could be a problem with one of the User-Defined DLLs or the CAD object. Are these custom DLLs that you created yourself or ones provided by others that are known to work? Improperly written DLLs can very easily crash OpticStudio if there is a bug in their code. For more information on creating proper DLLs, please see this Knowledgebase article: Custom DLLs in OpticStudio: An overview of user-defined surfaces, objects, and other DLL types – Knowledgebase (zemax.com).

Is the CAD object rather large or complex? Maybe try removing the CAD object, and the DLLs, one by one to see if you can narrow down the problem.

Best,
Ethan