This query is failing. Tell us at least three reasons why

select plan_id,
       t.medical_plan_description,
       medical_plan_name,
       medical_plan_type,
       medical_carrier_name
       min(month_key),
       max(month_key),
       count(*)
from source_data_table as mn
order by 1,2
group by 1,2,3,4,5,6

This query is failing. Tell us at least three reasons why.