how do correct error 'Expression does not produce a value' for populate a dropdownlist?

how do correct error 'Expression does not produce a value' for populate a dropdownlist?

Compiler Error Message: BC30491: Expression does not produce a value.
Line 43: <asp:DropDownList id=myddl runat="server" DataSource="<%#DataBind()%>" DataTextField="rptL1" DataValueField="rptL1">
Show Detailed Compiler Output:
...
target.DataSource = CType(DataBind(),Object)

my code for aspx.vb  is ...  

 Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
...
        If Not (Page.IsPostBack) Then
            MyDataBind()
            checkIfLocked()
            BindGrid()
        End If

Sub MyDataBind()
        myComm = New SqlDataAdapter("select rptL1 from rptDDL", MyConn)
        Dim myDS As DataSet = New DataSet
        myComm.Fill(myDS, "ddlscore")
        myddl.DataSource = ds.Tables("ddlscore")
myddl.DataTextField = "rptL1"
        myddl.DataValueField = "rptL1"
        myddl.DataBind()
    End Sub

Sub MyDataGrid_Update(ByVal Sender As Object, ByVal E As DataGridCommandEventArgs)
...
 Dim myddl As DropDownList
        myddl = E.Item.FindControl("myddl")

my code for aspx is ...

<EditItemTemplate>
<asp:DropDownList id=myddl runat="server" DataSource="<%#DataBind()%>" DataTextField="rptL1" DataValueField="rptL1"</asp:DropDownList>
</EditItemTemplate>