The datasource doesn't contain a datamember with the "duration" name - vb.net

Question

By using Dev express chart control am populating some of charts which are based on today,yesterday,week ,months and year based query.But the Problem is that am getting this error .
The datasource doesn't contain a datamember with the "duration" name.
where getDataset is global function which am using from last 6 months which is perfectly alright.plz help. help is appreciated
Here is my complete method
Protected Sub populateLoginHistoryChart(ByVal ddlSelectedValue As String)
Dim sqlQuery As String = Nothing
sqlQuery = "SELECT LT.LogOnTime AS duration , COUNT(*) AS posts "
sqlQuery += " FROM ( "
sqlQuery += "SELECT CASE"
sqlQuery += " When DATEPART(hh,[LogOnTime]) >= 0 AND DATEPART(hh,[LogOnTime]) <= 4 AND DATEPART(mm,[LogOnTime]) <= 59 then '00:00-04:00'"
sqlQuery += " When DATEPART(hh,[LogOnTime]) >= 4 AND DATEPART(hh,[LogOnTime]) <= 8 AND DATEPART(mm,[LogOnTime]) <= 59 then '04:00-08:00' "
sqlQuery += " When DATEPART(hh,[LogOnTime]) >= 8 AND DATEPART(hh,[LogOnTime]) <= 12 AND DATEPART(mm,[LogOnTime]) <= 59 then '08:00-12:00' "
sqlQuery += " When DATEPART(hh,[LogOnTime]) >= 12 AND DATEPART(hh,[LogOnTime]) <= 16 AND DATEPART(mm,[LogOnTime]) <= 59 then '12:00-16:00' "
sqlQuery += " When DATEPART(hh,[LogOnTime]) >= 16 AND DATEPART(hh,[LogOnTime]) <= 20 AND DATEPART(mm,[LogOnTime]) <= 59 then '16:00-20:00' "
sqlQuery += " When DATEPART(hh,[LogOnTime]) >= 20 AND DATEPART(hh,[LogOnTime]) <= 23 AND DATEPART(mm,[LogOnTime]) <= 59 then '20:00-23:00' "
sqlQuery += " End as LogOnTime "
sqlQuery += " FROM StudentLoginHistory"
If ddlSelectedValue = "Today" Then
sqlQuery += " WHERE DATEADD(dd, 0, DATEDIFF(dd, 0, LogOnTime)) = DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))"
sqlQuery += " )LT "
ElseIf ddlSelectedValue = "Yesterday" Then
sqlQuery += " WHERE DATEADD(dd, 0, DATEDIFF(dd, 0, LogOnTime)) = DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))-1 "
sqlQuery += " )LT "
End If
sqlQuery += " GROUP BY LT.LogOnTime"
sqlQuery += " ORDER BY duration"
If ddlSelectedValue = "Week" Then
sqlQuery = "SELECT CONVERT(varchar(25),LogOnTime,107) AS duration, count(*) AS posts"
sqlQuery += " FROM StudentLoginHistory WHERE "
sqlQuery += " DateDiff(Week,LogOnTime,GetDate())=1"
sqlQuery += " GROUP BY CONVERT(varchar(25),LogOnTime,107)"
sqlQuery += " ORDER BY duration"
ElseIf ddlSelectedValue = "Month" Then
sqlQuery = "SELECT LT.LogOnTime AS duration, COUNT(*) AS posts"
sqlQuery += " FROM (SELECT CASE "
sqlQuery += " When DATEPART(dd,[LogOnTime]) >= 1 AND DATEPART(dd,[LogOnTime]) <= 7 then '2013-05-01 to 2013-05-07'"
sqlQuery += " When DATEPART(dd,[LogOnTime]) >= 8 AND DATEPART(dd,[LogOnTime]) <= 14 then '2013-05-08 to 2013-05-14'"
sqlQuery += " When DATEPART(dd,[LogOnTime]) >= 15 AND DATEPART(dd,[LogOnTime]) <= 21 then '2013-05-15 to 2013-05-21' "
sqlQuery += " When DATEPART(dd,[LogOnTime]) >= 22 AND DATEPART(dd,[LogOnTime]) <= 28 then '2013-05-22 to 2013-05-28'"
sqlQuery += " End as LogOnTime "
sqlQuery += " FROM StudentLoginHistory"
sqlQuery += " WHERE(DatePart(mm, LogOnTime) = DatePart(mm, DateAdd(mm, -1, getdate())) AND DatePart(yyyy, LogOnTime) = DatePart(yyyy, DateAdd(mm, -1, getdate())))"
sqlQuery += " )LT "
sqlQuery += " GROUP BY LT.LogOnTime"
ElseIf ddlSelectedValue = "Year" Then
sqlQuery = "SELECT CONVERT(varchar(4),LogOnTime , 100) + CONVERT(varchar(4), LogOnTime, 120) AS duration,COUNT(*) AS posts"
sqlQuery += " FROM StudentLoginHistory WHERE "
sqlQuery += " year(LogOnTime) = year(DATEADD(year,-1,getdate())) "
sqlQuery += "GROUP BY CONVERT(varchar(4),LogOnTime , 100) + CONVERT(varchar(4), LogOnTime, 120) "
sqlQuery += "ORDER BY month(CONVERT(varchar(4),LogOnTime , 100) + CONVERT(varchar(4), LogOnTime, 120))"
End If
Dim ds As DataSet = objglb.getDataset(sqlQuery, "tbl")
Dim Title As New DevExpress.XtraCharts.ChartTitle()
Dim Diagram As XYDiagram = CType(LoginHistoryChart.Diagram, XYDiagram)
LoginHistoryChart.Titles.Clear()
Dim Series As New Series("Series", ViewType.Bar)
LoginHistoryChart.Series.Add(Series)
Series.DataSource = ds
Series.ArgumentDataMember = "duration"
Series.ValueScaleType = ScaleType.Numerical
Series.ValueDataMembers.AddRange(New String() {"posts"})
If ddlSelectedValue = "Today" Then
Title.Text = "Login History By Today"
ElseIf ddlSelectedValue = "Yesterday" Then
Title.Text = "Login History By Yesterday"
ElseIf ddlSelectedValue = "Week" Then
Title.Text = "Login History By Last Week"
ElseIf ddlSelectedValue = "Month" Then
Title.Text = "Login History By Last Month"
ElseIf ddlSelectedValue = "Year" Then
Title.Text = "Login History By Last Year"
End If
'the appearance of the X-axis title.
Diagram.AxisX.Title.Visible = True
Diagram.AxisX.Title.Alignment = StringAlignment.Center
If ddlSelectedValue = "Today" OrElse ddlSelectedValue = "Yesterday" Then
Diagram.AxisX.Title.Text = "Hours"
ElseIf ddlSelectedValue = "Week" Then
Diagram.AxisX.Title.Text = "Days"
ElseIf ddlSelectedValue = "Month" Then
Diagram.AxisX.Title.Text = "Weeks"
ElseIf ddlSelectedValue = "Year" Then
Diagram.AxisX.Title.Text = "Months"
End If
Diagram.AxisX.Title.TextColor = Color.Black
Diagram.AxisX.Title.Font = New Font("georgia", 12, FontStyle.Regular)
Diagram.AxisX.Range.Auto = False
'the appearance of the Y-axis title.
Diagram.AxisY.Title.Visible = True
Diagram.AxisY.Title.Alignment = StringAlignment.Center
Diagram.AxisY.Title.Text = "Logins Counts"
Diagram.AxisY.Title.TextColor = Color.Black
Diagram.AxisY.Title.Antialiasing = True
Diagram.AxisY.Title.Font = New Font("georgia", 10)
CType(Series.View, SideBySideBarSeriesView).ColorEach = True
LoginHistoryChart.Width = 900
LoginHistoryChart.Legend.Visible = False
LoginHistoryChart.Titles.Add(Title)
Title.Font = New Font("georgia ", 14)
End Sub

Answer 1

I don't see that you are setting the name of the table to bind to anywhere. I would change
Series.DataSource = ds
to
Series.DataSource = ds.Tables["tbl"]