When creating a report in GC, I go to add a form field and I get an invalid column headers pop-up, but I can't tell what is invalid about the column. When I click on the button to "Proceed to changes" it doesn't seem to provide instructions there either. When Editing Form Field, there are also no instructions about what characters will not work for reporting build. It would be helpful to have the list of invalid characters in at least one of these views.