![](https://uploads-us-west-2.insided.com/zemax-en/attachment/97237647-3dcf-4a5b-a8f8-b5870c714927.png)
I often get this message that does not allow me to undo (F3). I tied closing Zemax and re-opening it to see if it disappears but it does not.
I checked to see if such a file exists, and it does not exist. So I am not sure how to proceed. Please advice.