Most probably it is to do with one of the indicators, and again with high probability it is a custom one. Are you using custom indis?
If you remove it, it won't give an error no more. But you need to find it. If you can report it here, I can take a look and maybe fix it.
If you are able, then open the Indicators tab in the generator and test your custom indis by running a few of them at a time until you get that one causing the error.

I select all build in and all down loaded custom indicators. So, I may exclude all custom and remain the build in group of indicators to run generator.