Why OT_ESS.DATE is stated empty while calling DoSaveNow() althought it already has a value?

Here is the code in the submit button

Local Rowset &LocalRowOT;
&LocalRowOT = GetLevel0()(1).GetRowset(Scroll.OT_ESS);

For &i = ActiveRowCount(Scroll.OT_ESS) To 1 Step - 1
  
   If All(&LocalRowOT(&i).OT_ESS.EMP_RMK.Value) Then
      &LocalRowOT(&i).OT_ESS.STATUS.Value = "SUB";
   End-If;
   If All(&LocalRowOT(&i).OT_ESS.CODE.Value, &LocalRowOT(&i).OT_ESS.DATE.Value, &LocalRowOT(&i).OT_ESS.EMP_RMK.Value) Then
      &LocalRowOT(&i).OT_ESS.DATE.Enabled = False;
      &LocalRowOT(&i).OT_ESS.EMP_RMK.Enabled = False;
   End-If;
     
   DoSaveNow();
      
End-For;

I got this error messsage after click the SUBMIT_BTN
Field Is Required: OT_ESS - DATE

I try to display the value so add the code with message boxes:

Local Rowset &LocalRowOT;
&LocalRowOT = GetLevel0()(1).GetRowset(Scroll.OT_ESS);

For &i = ActiveRowCount(Scroll.OT_ESS) To 1 Step - 1
   MessageBox(0, "", 0, 0, "&i is " | &i | " &LocalRowOT(&i).OT_ESS.DATE is " | &LocalRowOT(&i).OT_ESS.DATE | " &LocalRowOT(&i).OT_ESS.DATE.Value is " | &LocalRowOT(&i).OT_ESS.DATE.Value);
End-For;

For &i = ActiveRowCount(Scroll.OT_ESS) To 1 Step - 1
  
   If All(&LocalRowOT(&i).OT_ESS.EMP_RMK.Value) Then
      &LocalRowOT(&i).OT_ESS.STATUS.Value = "SUB";
   End-If;
   If All(&LocalRowOT(&i).OT_ESS.CODE.Value, &LocalRowOT(&i).OT_ESS.DATE.Value, &LocalRowOT(&i).OT_ESS.EMP_RMK.Value) Then
      &LocalRowOT(&i).OT_ESS.DATE.Enabled = False;
      &LocalRowOT(&i).OT_ESS.EMP_RMK.Enabled = False;
   End-If;

   MessageBox(0, "", 0, 0, "before save : OT_ESS.DATE is " | OT_ESS.DATE | " and OT_ESS.DATE.Value is " | OT_ESS.DATE.Value);
     
   DoSaveNow();
      
End-For;

The first Message box
i is 1 &LocalRowOT(&i).OT_ESS.DATE is Field &LocalRowOT(&i).OT_ESS.DATE.Value is 2010-06-10

The second Message box
before save : OT_ESS.DATE is and OT_ESS.DATE.Value is

the field DATE already has a value (displayed in the message box). But why it generates error while calling DoSaveNow() ?