Object reference not set to a instance of an Object - vb.net

Question

I have a gridview that fills with data, and a view button which gives more details of the record choosen by the user. I cannot figure out why I am getting the error:
Object reference not set to a instance of an Object
I have narrowed it down to between my two message boxes. The First message box comes up but it crashes before the second. Any suggestions would be greatly appreciated.
Protected Sub CountAlerts_RowCommand(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs) Handles CountAlerts.RowCommand
If (e.CommandName = "Viewdtails") Then
Dim index As Integer = Convert.ToInt32(e.CommandArgument)
Dim NDC, Unit, Cell, DTTM, prod, Query, _startdt, _enddt As String
Dim DS As DataSet
NDC = CountAlerts.DataKeys(index).Values("NDC")
Cell = CountAlerts.DataKeys(index).Values("Cell")
Unit = CountAlerts.DataKeys(index).Values("Unit")
DTTM = CountAlerts.DataKeys(index).Values("TimeDate")
prod = CountAlerts.DataKeys(index).Values("ProductDesc")
_startdt = If(StartDate.Text = "", DateAdd(DateInterval.Day, -7, System.DateTime.Now).ToShortDateString, StartDate.Text)
_enddt = If(EndDate.Text = "", System.DateTime.Now.ToShortDateString, EndDate.Text)
For Each irow As GridViewRow In CycleCountAlerts.Rows
If irow.Attributes("class") = "highlight" Then
irow.Attributes.Remove("class")
End If
Next
CountAlerts.Rows(index).Attributes("class") = "highlight"
Query = " EXEC [Audits].[dbo].[ExceptionDetailsCombined] '" & NDC & "', '" & Cell & "', '" & Unit & "', '" & DTTM & "', '" & Master.CF_User.Viewing & "' "
DS = SelectQuery(Query)
If (DS.Tables.Count > 0) Then
unitbox.Text = DS.Tables(0).Rows(0)("Unit")
cellbx.Text = DS.Tables(0).Rows(0)("Cell")
ndcbox.Text = DS.Tables(0).Rows(0)("NDC")
namebox.Text = DS.Tables(0).Rows(0)("ProductDesc")
cycdttmbx.Text = DS.Tables(0).Rows(0)("TimeDate")
cycusr.Text = DS.Tables(0).Rows(0)("CycUser")
todisp.Text = DS.Tables(0).Rows(0)("TODISPSIZE")
topkgbox.Text = DS.Tables(0).Rows(0)("TOPKGSIZE")
toqtybx.Text = DS.Tables(0).Rows(0)("TOQTY")
FRQTYbx.Text = DS.Tables(0).Rows(0)("FRQTY")
TextBox2.Text = DS.Tables(0).Rows(0)("ActualQTY")
cycvarqbox.Text = DS.Tables(0).Rows(0)("CYCLEVARQTY")
CycleVarPctbx.Text = DS.Tables(0).Rows(0)("CYCLEVARPCT")
alertrsnbx.Text = DS.Tables(0).Rows(0)("AlertReason")
combox.Text = DS.Tables(0).Rows(0)("AcceptComment")
acusr.Text = DS.Tables(0).Rows(0)("AcceptUser")
acctime.Text = DS.Tables(0).Rows(0)("AcceptTime")
accstatbx.Text = DS.Tables(0).Rows(0)("AcceptStatus")
displbl.Text = DS.Tables(0).Rows(0)("Disposition")
End If
Query = " EXEC [CF_Audits].[dbo].[CommentTrackerCombined] '" & Master.CF_User.EmployeeID & "', '" & NDC & "', '" & Cell & "', '" & Unit & "', '" & _startdt & "', '" & _enddt & "', '" & Master.CF_User.Viewing & "' "
DS = SelectQuery(Query)
If (DS.Tables.Count > 0) Then
ExceptionHist_GV.DataSource = DS
ExceptionHist_GV.DataBind()
ExceptionHist_GV.UseAccessibleHeader = True
MsgBox("except gv header") 'Runs up to here.
ExceptionHist_GV.HeaderRow.TableSection = TableRowSection.TableHeader
MsgBox("except gv header 2") ' Does not make it to here.
End If
End If
End Sub

Answer 1

Most likely TableRowSection or TableRowSection.TableHeader is/are Nothing
Check that these are initialised before using them
If MsgBox("except gv header")
If Not TableRowSection Is Nothing AndAlso Not TableRowSection.TableHeader Is Nothing Then
ExceptionHist_GV.HeaderRow.TableSection = TableRowSection.TableHeader
Else
MsgBox "How did we get here?"
End If
MsgBox("except gv header 2")
If you see the message "How did we get here" that indicates you have not initialised you object

Answer 2

In object orientated languages you need to instantiate an object before you can use it.
Something in this line:
ExceptionHist_GV.HeaderRow.TableSection = TableRowSection.TableHeader
has not been instantiated with the new keyword. You can find out exactly what by checking the details of the Exception which was thrown.
It will be either ExceptionHist_GV or TableRowSection.