Try:
... from tbl_ProductDetails PD left join tbl_PurchaseMaster PM on PD.Prod_ID=PM.Prod_ID left join tbl_SaleMaster SM on PD.Prod_ID=SM.Prod_ID ...
OR
from tbl_ProductDetails PD left join tbl_PurchaseMaster PM on PD.[Prod_ID]=PM.[Prod_ID] left join tbl_SaleMaster SM on PD.[Prod_ID]=SM.[Prod_ID]
Square brackets around the whole columname might be confusing and have no reference which table they are from.