问将DataType varchar转换为数字的错误

EN

'NULL' AS DATE (in 1st query of this SP)------(1)
CONVERT(VARCHAR, tbl_IPD.ipd_doa, 103) AS DATE (in 2nd query of this SP)-----(2)

SELECT 
   tbl_CompanyProfile.Company_Name, tbl_CompanyProfile.Company_Address, 
   tbl_CompanyProfile.Company_ContactNo, tbl_CompanyProfile.Company_Email, 
   tbl_CompanyProfile.Company_Website, 
   'NULL' AS NAME, 'NULL' AS DATE,
   'NULL' AS AMOUNT, 'NULL' AS DEPARTMENT, 
   0 AS Age, @from AS StartDate, @to AS EndDate
FROM 
   tbl_CompanyProfile

UNION ALL

SELECT   
   '--', '--',
   '--', '--', '--', 
   tbl_IPD.ipd_pfname + ' ' + tbl_IPD.ipd_plname AS NAME, 
   CONVERT(VARCHAR, tbl_IPD.ipd_doa, 103) AS DATE, 
   ISNULL(SUM(tbl_fee.fee_amount), 0) AS AMOUNT, 
   tblDepartment.DeptName AS DEPARTMENT, tbl_IPD.ipd_age AS Age,  
   @from AS StartDate, @to AS EndDate
FROM            
   tbl_fee 
LEFT OUTER JOIN
   tbl_IPD ON tbl_fee.ipd_id = tbl_IPD.ipd_id 
LEFT OUTER JOIN
   tblDepartment ON tbl_IPD.ipd_dpt = tblDepartment.DeptId 
WHERE        
   (tbl_IPD.ipd_doa BETWEEN @from AND @to)
GROUP BY 
    tbl_IPD.ipd_pfname, tbl_IPD.ipd_plname, tbl_IPD.ipd_doa, tblDepartment.DeptName, tbl_IPD.ipd_age