"Item has already been added - key indexed (or 'in dictionary'?) 0, Key being added '0' - When viewing a window

Version 2
    Issue

    You get the following error when trying to view a particular window:  "Item has already been added - key indexed (or 'in dictionary'?) 0, Key being added '0'

     

     

    Cause

    The issue is caused by either:

     

    • Invalid collections, usually on the Group object but can be anywhere

     

    • Incorrect tabbing order on the window - turn automatic tabbing off, save, turn it on, test.

     

    • Another unknown problem with the window, in which case contact your support provider

    Environment

    7.x