Error 72: Unknown error after exploding CAD Parts

  • 28 April 2023
  • 3 replies

I have some issues importing step files to OpticStudio and exploding it. The step file works fine until exploding. After exploding it says “Error 72: Unknown Error” in the Shaded Model.

I never had this issue before although I often work with step files and exploding them. I discovered that for files that work after explosion, there are 3 new files in the CAD Files folder (.stp_1.ZAN, .stp_1.SAB, .stp_1.SAB txt file). When Error 72 shows up after exploding there is only .stp_1.SAB in the directory.

Sometimes the first 5 parts for example have these 3 files after exploding and the last 5 don’t. If I delete the last 5 parts in the simulation the Error disappears. 

Has anyone ever had this error and can help?


Best answer by Sandrine Auriol 3 May 2023, 12:02

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Userlevel 6
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The error 72 is due to the ACIS CAD libraries that were implemented in OpticStudio 20.3. Previous OpticStudio all use SMS CAD libraries. As we are investigating new CAD libraries, we recommend now to untick these ones and work with the SMS CAD libraires.
To do that, click Project Preferences...General and untick Use ACIS Libraries:


In the newest version of Optics studio this fix is not working.


After unchecking the ACIS libraries box, Zemax freezes and the.step file doesn’t even get loaded. 

Can anyone recommend another fix? This is extremely frustrating as the CAD files had no issues earlier!


Userlevel 7
Badge +2



You may want to share a CAD file for troubleshooting. Also, it might be helpful to know up until which version did the CAD file load properly.

Take care,