Error in sub report of crystal report in Formula Field

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C#

CrystalReports

Hello,

I am making a sub report in Crystal Report using coding.One error come in Formula field that i can not understand because of all the things are perfact. so please help me...

Formula Field.:

if {Command.opbal}<0 then "Dr." Else "Cr."

error like : This field name is not known. Error in File C:\Users\user\AppData\Local\Temp\Debtors_Total_Outstanding_Report {A682B99D-A38B-43F3-BB05-63C258E9E0E2}.rpt: Error in formula . 'if {Command.opbal}<0 then 0 else {Command.opbal}' This field name is not known.

when click on Report.

i use command button like :

select *  from {?database}.dbo.AC_LEDGER

the main report i bind like :

                string str = "select crbal*-1 as crbal, glname, glcode,contprsn, refby, glphone1, glcity, glphone2, email, crlimit, restorddueamt  from glmast WHERE drgroup='A3402' and crbal<>0 and glcode in(" + strSelection + ")";
                SqlDataAdapter ad = new SqlDataAdapter(str, con2);
                DataSet ds = new DataSet();

                ad.Fill(ds);

                path = Server.MapPath("Debtors_Total_Outstanding_Report.Rpt");
                cr = new ReportDocument();
                cr.Load(path);
                
                cr.SetDataSource(ds.Tables[0]);
           
                
                cr.SetParameterValue(0,ds.Tables[0].Rows[0][1].ToString());
                cr.SetParameterValue(1,company_name);
                cr.SetParameterValue(2, database_name);


               
                CrystalReportViewer1.ReportSource = cr;
                CrystalReportViewer1.DataBind();
so, please help me.


Thanks and Regards,
Mitesh