Problem adding Formula field

Problem adding Formula field

Hi,
I am trying to add a Formula field but I get the error "An unexpected error has occured. Kindly refresh the page"

My application is http://zohocreator.com/leejordan/elections. I have shared it with support@zohocreator.com

On the Elections tab I am trying to add a formula field that references a Form - Single Select field ie $Electing_Operators.

Thanks

Lee.