Access denied when a user click ‘Add document’

I have recently received random reports from users that they are presented with an access denied message when trying to upload files to a document library by clicking the ‘Add document’ link:

The permissions all looked fine so I turned to the logs.  It transpires that the Content Organizer feature had just been enabled on the site that contained these document libraries, which utilises a document library named Drop Off Library.  The users had no access to this library, hence the message above.

In this instance I just disabled the feature as it is not required, so the problem went away.  Otherwise I would have changed the permissions on the Drop Off Library.