Field Explorer
formula field
right click select new
if table.field=0 then 'YES' else if table.field=1 then 'NO' else 'ERROR'
Or place the field on the report
right click on it
select format field
Common tab
display string formula box
if currentfieldvalue=0 then 'Yes' else if currentfieldvalue=1 then 'No' else 'Error'