Error converting data type nvarchar to bigint.

hi all

i used this t-sql codes

SELECT PAH.TypeRef,PAH.ProductActionHeaderNum,PAH.ProductActionHeaderDate,PAH.AccountDetailRef
 ,AD.AccountDeatil
 ,PAH.StorageRef ,S.StoragesName 
 ,PAH.ProductActionHeaderComment
 ,PAH.SendDocNum
 ,PAI.ProductRef,P.ProductName,U.UnitName,PAI.Quanty
  FROM dbo.ProductActionHeader PAH 
 INNER JOIN dbo.ProductActionItem PAI ON PAH.ProductActionHeaderId=PAI.ProductActionHeaderRef 
 INNER JOIN dbo.AccountDetail AD ON AD.AccountDetailId=PAH.AccountDetailRef
 INNER JOIN dbo.Product P ON P.ProductId =PAI.ProductRef 
 INNER JOIN dbo.Unit U ON U.UnitId=P.UnitRef
 INNER JOIN DBO.Storages S ON S.StoragesId =PAH.StorageRef 
 WHERE PAH.TypeRef=1   AND P.HasPrice=0
 UNION
 SELECT PAH.TypeRef,PAH.ProductActionHeaderNum,PAH.ProductActionHeaderDate,PAH.AccountDetailRef
 ,AD.AccountDeatil
  ,PAH.StorageRef ,S.StoragesName 
  ,PAH.SendDocNum
 ,PAH.ProductActionHeaderComment
 ,PAI.ProductRef,P.ProductName,U.UnitName,PAI.Quanty 
  FROM dbo.ProductActionHeader PAH 
 INNER JOIN dbo.ProductActionItem PAI ON PAH.ProductActionHeaderId=PAI.ProductActionHeaderRef 
 INNER JOIN dbo.AccountDetail AD ON AD.AccountDetailId=PAH.AccountDetailRef
 INNER JOIN dbo.Product P ON P.ProductId =PAI.ProductRef 
 INNER JOIN dbo.Unit U ON U.UnitId=P.UnitRef
  INNER JOIN DBO.Storages S ON S.StoragesId =PAH.StorageRef 
 WHERE PAH.TypeRef=2 AND    P.HasPrice=0
 ORDER BY  PAH.ProductActionHeaderDate,PAH.ProductActionHeaderNum,PAH.TypeRef,PAI.ProductRef

but i see this error

Msg 8114, Level 16, State 5, Line 2
Error converting data type nvarchar to bigint.

how to solve it

thanks

Name of Allah, Most Gracious, Most Merciful and He created the human