Y-axis value bounding error in ASP.NET Chart controls

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chart

ASP.NET4

I am using ASP.NET Chart control.
while executing i am getting the below error.
Error : "Y values cannot be data bound to the string object.Parameter name: yValues"
What is the problem in the above error.

See my code:
-------------
If dtable.Rows.Count > 0 Then
Dim xvalue As New List(Of String)()
Dim yvalue As New List(Of String)()
For i As Integer = 0 To dtable.Rows.Count - 1
xvalue.Add(dtable.Rows(i)("Emp_ID"))
yvalue.Add(dtable.Rows(i)("Section"))
Next
Dim xvalues As String() = xvalue.ToArray
Dim yValues As String() = yvalue.ToArray
Chart1.Series("ColChart").Points.DataBindXY(xvalues, yValues)
''Error displaying here -Y values cannot be data bound to the
string object.

End if