How to Fix Login Failed For User NT AUTHORITY IUSRS in SharePoint 2013 Business Connectiity Services
If you have created an external content type and are trying to access it in a list and get "AccessDenied" then that is because you have not given permissions to the logged in user to use that external content type. You can easily give permissions to that user or to all users in your site by going to the Central Administration site and configuring the business connectivity service. For the exact procedure of how to do it read the following. SharePoint 2013 Business Connectivity Service Access DeniedError: http://mosshosting.asphostportal.com/?p=2650 Some users get another very interesting error message after they have assigned permissions on the external content type. The error message is: Message from ExternalSystem: "Login failed for user 'NT AUTHORITY\IUSR'.". This error occurs because the database does recognize the credentials passed from SharePoint. Which database? The database that you are connecting to in your external content type! It