Get the value of checkbox column

I want to get the value of check box value on the Document Printing, I can get the value of other columns but it show only 0 even if it's checked on unchecked. Anyone knows what's wrong?

Here is my code:

Dim oForm As SAPbouiCOM.Form

Const mGrid = "6"

Public Sub ItemEvent(oForm As SAPbouiCOM.Form, pVal As SAPbouiCOM.IItemEvent, _

    nBubble As Integer)

If ((pVal.FormType = XX_CHECKREISSUE And pVal.EventType = et_ITEM_PRESSED)) Then

    If pVal.ItemUID = "1" And (pVal.BeforeAction = True) Then

    Dim mtrx As SAPbouiCOM.Matrix

    Set mtrx = oForm.Items(mGrid).Specific

    MsgBox (mtrx.Columns(0).Cells(1).Specific.Value)

    End If

End If

End Sub