Incorrect syntax near the keyword 'AND'. why?

Dim SampleOrder As String = Nothing
        Dim Requester As String = Nothing
        Dim ProjectNumber As String = Nothing
        Dim CostCenter As String = Nothing
        Dim PersonInvoiced As String = Nothing
        Dim SelectQuery As String = "SELECT [OrderID], [DVMOrderNumber], [Requester], [ProjectNumber], [CostCenter], [CostResponsable], [CostCategory], [TotalSamples], [OrderDescription], [FinalCustomerAddress], [TargetDate], [AssemblyPlannedDate], [LogisticsResponsable], [ShippingMode], [ShippingAddress], [Urgent], [HasBOM], [HazardousMaterial], [ExpressShipment], [HasSerialComponents], [PrototypeComponents], [OrderType] FROM [Orders_Header]"
        Dim WhereQuery As String = Nothing

        Requester = BOX_Requester1.Text
        Requester = Find.Find2(Requester)

        If Requester <> Nothing Then
            WhereQuery = WhereQuery & " AND Requester LIKE '" & Requester & "'"
        End If

  

        Dim myQuery As String = SelectQuery & WhereQuery
        SqlDataSource2.SelectCommand = myQuery
        GridView1.DataSourceID = "SqlDataSource2"
        GridView1.DataBind()

        If GridView1.Rows.Count = 0 Then
            LBL_Error.Visible = True
            LBL_Error.Text = "I have not found any results by your search!"
            LBL_Status.Text = String.Empty
        Else
            LBL_Status.Visible = True
            LBL_Status.Text = "Dates have been loaded! Found " + Convert.ToString(GridView1.Rows.Count) + " rows."
            LBL_Error.Text = String.Empty
        End If