Cannot specify a sql CLR type in a Schema-bound object or a constraint expression - SQL - WITH SCHEMABINDING

Question

I have a UDF function and I found some tips to get better performance:

https://www.mssqltips.com/sqlservertip/5864/four-ways-to-improve-scalar-function-performance-in-sql-server/

I tried them all but I cannot get 'WITH SCHEMABINDING' to work. Error: 'Cannot specify a sql CLR type in a Schema-bound object or a constraint expression'

Why does this mean ?

My code

    ALTER FUNCTION [SIF_get_SalesAmountDosMain1] 
(
    -- Add the parameters for the function here
      @DossierCode   T_Code_Dossier 
)
RETURNS T_Fin_Amount
--WITH RETURNS NULL ON NULL INPUT
WITH SCHEMABINDING
AS
BEGIN

    DECLARE  @DetailCode       T_Code_Detail 
          ,  @DetailSubCode    T_Code_DetailSub
          ,  @TotalSalesAmount T_Fin_Amount
          ,  @SalesAmount      T_Fin_Amount

    Select  @TotalSalesAmount = 0

    DECLARE
            Cur_DosMain CURSOR LOCAL FORWARD_ONLY STATIC FOR
            SELECT  DetailCode
            ,       DetailSubCode
            FROM dbo.T_DossierDetail
            Where   DossierCode = @DossierCode
            FOR READ ONLY

    OPEN Cur_DosMain

    FETCH Cur_DosMain   INTO    @DetailCode, @DetailSubCode

    WHILE (@@FETCH_STATUS = 0)
    BEGIN

            SELECT dd.DetailCode,dd.DetailSubCode
            FROM dbo.T_DossierDetail dd
            Inner Join dbo.T_Part p on p.PartCode = dd.PartCode
            Where  dd.DossierCode = @DossierCode

        Select @TotalSalesAmount = @TotalSalesAmount + IsNull(@SalesAmount, 0)
        
        FETCH Cur_DosMain   INTO    @DetailCode, @DetailSubCode
    End

    CLOSE Cur_DosMain
    DEALLOCATE Cur_DosMain

    -- Return the result of the function
RETURN  @TotalSalesAmount 

END
                                                                                                                                                                                                    
GO

Answer 1

Found it:

I was using types like T_Code_detail and T_Fin_Amount

changing them in nchar(3) and numeric(14,2) did the trick.