Google Picker in Apps Script Web App gives some users 403

[Stephen Hind]

We have a gadget that's been working for years where it initiates the Google Picker to allow users to upload an image to use.  The Picker does not show anything from users' Drives, just the ability to upload.  

We get the OAuth token for Picker from Apps Scrpt's  ScriptApp.getOAuthToken() but since Friday some users are getting 

403, That's an error

We're sorry, but you do not have access to this page. That's all we know.

Has Google silently changed something that could cause this to happen?  Any ideas greatly appreciated.

[Stephen Hind]

On further investigation The Picker still appears to work for the Effective User and not other Active Users: has something changed in Picker so it no longer accepts the Effective User's token?

[Stephen Hind]

This appears to be a wider issue and there's an open issue for it:

• 403 Error - We're sorry, but you do not have access to this page Issue when calling PickerBuilder to attach file