Freeform Drag and Drop Submission Error

Hi all,

I've built a freeform drag-and-drop knowledge check in SL, and for some reason though I've triggered the screen to submit after the objects have all been dropped on their targets, in the Preview I'm getting a pop up that says "Invalid" after each item is dropped on its correct target. Why is this happening? How should the triggers be set to only submit the D/D after ALL items have been dropped on their targets? And, then, how should I trigger the "Correct" layer to be shown after all objects have made their correct targets? Thank you!