This is the code :

```
let theBoard = self.storyboard!
let vc = theBoard.instantiateViewControllerWithIdentifier("myViewId")  as! UIViewController // this line causes the error

```

The second line causes this error:

```
unexpectedly found nil while unwrapping an Optional value

```

**\* VERY IMPORTANT \*** : the error only fires when the build configuration is set to "`debug`". It works well when set to "`release`".

Why ?