UI Application cannot update GL account in AR Credit memo

Hi,

B1 version 8.82 PL12

I am creating a UI application in AR Credit Memo.  I have 2 scenario for users to choose and each scenario will change the default GL account in AR credit memo.

1 scenario:  Real Return Goods

2 scenario:  correction of AR invoice

However, i find that the following statement cannot update in program.  It won't pop up the error message just won't overwrite the default GL account setting in GL determination.

oMatrix.Columns.Item("29").Cells.Item(j).Specific.value = "550111300"

Is there anything wrong with my statement above?

Please help.

Regars,

Anna

Program Logic:

If BusinessObjectInfo.FormTypeEx = "179" And BusinessObjectInfo.EventType = SAPbouiCOM.BoEventTypes.et_FORM_DATA_ADD And BusinessObjectInfo.Type <> "112" Then

If BusinessObjectInfo.BeforeAction = False And BusinessObjectInfo.ActionSuccess = True Then
          oForm = SBO_Application.Forms.Item(BusinessObjectInfo.FormUID)
          oMatrix = oForm.Items.Item("38").Specific

If SBO_Application.MessageBox("Return or Correction?", 1, "Return", "Correction") = 1 Then
              'return
               oForm.Freeze(True)
               oMatrix.Columns.Item("29").Cells.Item(1).Click()
For j As Integer = 1 To oMatrix.RowCount - 1
               oMatrix.Columns.Item("29").Cells.Item(j).Specific.value = "550111300"
               Next
               oForm.Freeze(False)
Else
              'correction
               oForm.Freeze(True)
               oMatrix.Columns.Item("29").Cells.Item(1).Click()
For j As Integer = 1 To oMatrix.RowCount - 1
               oMatrix.Columns.Item("29").Cells.Item(j).Specific.value = "550111100"
Next
               oForm.Freeze(False)
End If
  End If
     End If