So I get this.  The Column type is a Drop List, however even after creating a new Column (Text/Number), adding the same formula which works, I get the same error.  
This is my formula:
=LEFT([Final "SEVERITY" Code Assigned:]1, 1) + LEFT([Final "PROBABILITY" Code Assigned:]1, 1)
Final "SEVERITY" Code Assigned: = "1-Catastrophic, Final "PROBABILITY" Code Assigned: = A-Frequent.  Result: 1A
What can I do to convert successfully to Column Formula?