SELECT pmc.[month]                                    AS 'Month',
       pmc.pd_name_of_project                         AS 'Name of Project',
       tbl_div.name                                   AS 'Name of Advisory Services Division',
       TBL_PMC_UNIT.UNIT_NAME                         AS 'Name of Unit',
       pmc.staff_engineers,
       pmc.staff_clerical,
       pmc.staff_peons,
       pmc.pd_project_type                            AS 'Project Type',
       pmc.accepted_tender_cost                       AS 'Accepted Tender Cost',
       pmc.work_order_date                            AS 'Work Order Date',
       pmc.tender_period_months                       AS 'Tender Period',
       pmc.project_completion_date                    AS 'Project Completion Date',
       pmc.per_pmc_charges                            AS '% Of PMC Charges',
       pmc.total_pmc_charges_scheme                   AS 'Total PMC amount   of the Scheme',
       pmc.bill_amount_certified_upto_previous_month  AS 'Bill amount certified upto previous Month',
       pmc.total_PMC_charges_upto_previous_month      AS 'Total PMC charges  upto previous Month',
       pmc.receipt_PMC_charges_upto_previous_month    AS 'Receipt of PMC Charges upto previous Month',
       pmc.balance_of_PMC_charges_upto_previous_month AS 'Balance of PMC charges upto previous Month',
       pmc.bill_amount_certified_current_month        AS 'Bill amount certified During Current Month',
       pmc.PMC_charges_for_current_month              AS ' PMC charges  During Current Month',
       pmc.receipt_PMC_charges_current_month          AS 'Receipt of PMC Charges During Current Monthh',
       pmc.balance_of_PMC_charges_current_month       AS 'Balance of PMC charges During Current Month',
       SUM(pmc.salary_allowance)                      AS 'Salary Allowance'
FROM   TBL_PMC pmc
       INNER JOIN TBL_DIV
         ON TBL_DIV.ID = pmc.DIV_ID
       LEFT OUTER JOIN TBL_PMC_UNIT
         ON TBL_PMC_UNIT.ID = pmc.UNIT_ID
WHERE  pmc.div_id = 17
GROUP  BY pmc.[month]; 

Esta consulta está me dando o erro:

A coluna 'TBL_PMC.pd_name_of_project' é inválida na lista de seleção porque não está contida em uma função agregada ou na cláusula GROUP BY.