I've got a client script that I want to use with an externally available suitelet. In the suitelet I call

form.clientScriptModulePath = './external_schedulerClient.js';

and get the following error:

Permission Violation: You need the 'Lists -> Documents and Files' permission to access this page. Please contact your account administrator.

I've created a role for that suitelet to run as, and have given that role that particular permission. What am I missing?