One of the very few cases/scenarios where running validation on the model layer *before* rendering/user input as well as after probably would have given better error description at the cost of more code running / less perceived performance.

>This confirms I have resolved the issue.
>
>This was when the user tried to access a form where two selected=true was being done. This was a side effect of an adjustment needed in a merge process. Duplicate records were created. And, on those duplicates, one was at least applicable to selected=true.