The array rank reduction error is due to your script trying to write an Empty List to a string parameter value. You need to set up a filter before the Element.SetParameterByName node using List.IsEmpty and List.FilterByBoolMask to remove the elements/values that are empty lists (do not have a keynote value assigned)
I found your .dyn file on your previous post and I’ll assume this post of yours is also the same topic - it is best not to create duplicate posts seeking the same solution; if you haven’t received feedback on something then add more information to the initial post instead, i.e. upload a sample Revit and Keynote file that contains families that are causing errors. Adding more to your previous posts would bump them back up in the forum’s feed as well as give other people more information to help you with.