@sdetweil In case anyone finds this post in the future.
This problem is usually one of two causes:
The google apps script was not deployed correctly and the request runs into a permission error page There is an error in the request due to bad script URL or other parameterI have updated the module to fail gracefully in these cases and hopefully provide a better error message. If you are still having problems feel free to add an issue to the repo. (https://github.com/ryan-d-williams/MMM-GoogleSheets/issues).