error message appears when I clicked 'all tech please' at the start

https://imgur.com/a/WujqIQi

What Factorio version are you using? I can't reproduce it with Factorio 1.1.5

I made it crash on the same line on purpose and noticed that the line number for sandbox.lua is different (in your picture it's 71, for me it is 72), Did you edit that file?
I know why it is crashing, but the thing is it should be impossible for that field to be nil and fixing the crash almost certainly will lead to another one a few lines later etc.

As strange as it may sound, can you upload a save after you started the sandbox scenario and before clicking the button?

1.1.5

I did not edit the file. I am kicked out of the scenario after the error happens

I need a save file after you started the scenario, before clicking any buttons. Maybe it could be an interaction with mods (i tried with Krastorio 2 and Informatron, Factory Planner and Module Inserter), still no crash.

here is a .zip of the scenario folder's save file. I updated to 1.1.6. the error persists.
https://drive.google.com/file/d/1t3GcsOBXzP7IguxuMn6GKQl4ck_Mxyuc/view?usp=sharing

Okay, that helped, thanks. Should be fixed in the latest version.

You will get another error when you click the "Items please" button, but that is because the sandbox.lua is from when you created the scenario (1.0 i think) and somehow didn't get updated.

To fix it copy the sandbox.lua from Factorio/base/scenarios/sandbox into your custom scenario and it should work

cheers