Yup, looks like gmail doesn't like this script. I'll review it to see if I made some mistakes while trying to meet the last user's "special needs", but it's possible things have changed on Google's end.
... I did see that I'd accidentally uploaded a version that checks gmail every second (which is BAD), but even when I try to check my mail once I'm getting an authorization error.
I'll look into it and get back to you.