Welcome to the community! You should be able to understand this more clearly if you download your survey form as an xlsform as outlined here.
Once you have downloaded your xlsform you should see 3 different sheets (survey, choices and settings). The first one being the survey tab. On the survey tab, go to row 10. you should see either a select_one vc4am72 or a select_multiple vc4am72 question type. Here you are trying to select the choices from the choices tab list_name defined as vc4am72 which is accidentally not present in the choices tab. Try defining the choices there and your problem should be solved.
Here is a workaround on how it affects:
You should see a similar error message if you design your survey form as shown in the image below:
Thank-you for your helpful response.
So far, I have set up my first survey typing straight into kB toolbox. You suggest I convert it to an XLsform. A) how do I do that? & b) can I correct the error directly into the kbtoolbox form creator (& if so, is there an easy way to know which is row 10) or do I need to do it with n the xlsform?
Have a look at this post. It should help you download your survey project in an xlsform:
Regarding your first query:
You could make corrections directly from the KoBoToolbox form builder as well. But the risk here is that you may not know which question stands in row 10. The best and easy option would be scanning and editing your survey project by downloading them to an xlsform and then making changes. After making changes, you could redeploy them again.