Forms Data Controls ::How To Get Formview DropDownList In Updatepanel

Hi, i am newbie to asp.net. In my page there is a formview with sqldatasource. In which there is a dropdownlist wrapped with an updatepanel. What i'm trying to do is the re-bind ddlStudents after adding new row to the students table (using gridview and
ajax popup extender-both working fine, i'm being able to add new )

<asp:UpdatePanel ID="ddlUpdatePanel" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:DropDownList ID="ddlStudents" runat="server"
DataSourceID="sdsStudents"
DataValueField="studentID"
DataTextField="name"
SelectedValue='<%# Bind("studentID") %>' >
asp:DropDownList>
</ContentTemplate>
</asp:UpdatePanel>
<asp:SqlDataSource ID="sdsStudents" runat="server"
ConnectionString="<%$ ConnectionStrings:myConnectionString %>"
SelectCommand="SELECT studentID, name FROM tblStudents">
</asp:SqlDataSource>
after closing the popup,
Protected Sub btnClose_Click(ByVal sender As Object, ByVal e As EventArgs)
If IsPostBack Then
ddlUpdatePanel.Update()
ddlStudents.DataSourceID = "sdsStudents"
ddlStudent.DataBind()
modalPopupPanel.Hide()
End If
End Sub

I am getting error;

Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control.