I have a web part using an external list through an external content type which uses Business Data Connectivity with SQL Server Authentication through the use of a Secure Store Service key. Everything works fine until I try to access the page I'm using the list on with a user who isn't the site owner.
The first error I got was about Business Data Connectivity permissions so I went in and added my test user to the BCD permissions list and gave him Execute permission. That, I think, should allow him to use the web part with the external list IF I were connecting to the database with user authentication.
However, in my case, since I'm using SQL authentication through a Secure Store Service key, I get an error about that key entry which is completely unhelpful. I first figured it was another permissions issue so I added my test user to the "Target Application Administrators" of the key which, first off: doesn't seem right that every user would have to be an administrator for the key, and second: still just doesn't work. Anyone have an idea? I would post the error I get but it literally tells me nothing other than mentions the name of my Store Service Key and gives me a long, meaningless stack trace.