The parent list is not selected for this cascaded list

Cascaded lists are lists that re-load the items based on selection in another(parent) list

(1)Parent List (2)Child List

This error is shown when you have created a cascaded list but there is no parent list selected.

Double-click the child list to open the properties box. In the properties box, select the parent list.
OR
If this is not meant to be a cascaded list, uncheck the 'cascaded' option.