I just realized what the issue is:

This is not an error. The panel under your formula editor is trying to evaluate the value of your formula. This is not always possible. In this case, it doesn't have a way to know which row to show, so it has no "scope". This is only used for troubleshooting, and will not affect your application.
When a formula can be evaluated, it will display the result:

In this case, I am asking for the field of a selected row, so it can properly evaluate the result.