iOS app (this class is not key value coding-compliant for the key dataSource)

This error usually occur when outlets are not connected properly. In my case checking outlets connection would always solve it.

It looks like you've wired things up in interface builder incorrectly. It appears you have attached something to an outlet called dataSource in your SessionsTableViewController. It looks like you probably wanted to do it the other way round as I assume you have a table view in SessionsTableViewController.

So, you need to attach the dataSource property of your table view to your instance of SessionsTableViewController (probably "File's Owner" in your case), rather than the other way round.