Error with PopupControlExtender Microsoft JScript runtime error: Sys.ArgumentUndefinedException: Value cannot be undefined. Parameter name: type

hi ,

I've been trying to make a grid with some data from a database and when I hover or click on a certain column I want a PopupControlExtender to appear and give me extra information.

I am trying to do something similar to this. Except I dont want to use an magnifying image, I just want to hover over a column(for example Product Name column) 

However everytime I hover over the column I keep getting this error

Microsoft JScript runtime error: Sys.ArgumentUndefinedException: Value cannot be undefined.
Parameter name: type

I can't seem to find anything that helps me, I've been trying to debug this for a day now and got nothing. Can anyone help me?

my markup:

<%@ Page Title="Tracking Tool" Language="VB" MasterPageFile="~/Site.Master" AutoEventWireup="true"
    CodeFile="Default.aspx.vb" Inherits="_Default" %><%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %><asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent"></asp:Content><asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent"><asp:ToolkitScriptManager ID="ScriptManager1" runat="server"></asp:ToolkitScriptManager><asp:Label ID="Lbl_MaterialType" runat="server" Text="Material Type:"></asp:Label><asp:DropDownList ID="Ddl_MaterialType" runat="server" OnSelectedIndexChanged="Ddl_MaterialType_SelectedIndexChanged" AutoPostBack="True"></asp:DropDownList><asp:GridView ID="Gvw_Batches" runat="server" CssClass="Grid" AutoGenerateColumns="False"  OnRowDataBound="Gvw_Batches_RowDataBound" OnRowCommand="Gvw_Batches_Rowcommand" OnRowUpdating="Gvw_Batches_RowUpdating" OnSelectedIndexChanged="Gvw_Batches_SelectedIndexChanged"  onrowcreated="Gvw_Batches__RowCreated" ><Columns><asp:ButtonField  Text="SingleClick"  CommandName="SingleClick"  Visible="false"   />    <asp:TemplateField HeaderText="ORIGREC" Visible ="false" ><ItemTemplate><asp:Label ID="ORIGRECLabel" runat="server" Text='<%# Eval("ORIGREC") %>'></asp:Label><asp:TextBox ID="ORIGREC" runat="server" Text='<%# Eval("ORIGREC") %>' Width="175px" visible="true"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Material Code"  ><ItemTemplate><asp:Label ID="MATCODELabel" runat="server" Text='<%# Eval("MATCODE") %>'></asp:Label><asp:TextBox ID="MATCODE" runat="server" Text='<%# Eval("MATCODE") %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Material Name"  ><ItemTemplate><asp:Label ID="MATNAMELabel" runat="server" Text='<%# Eval("MATNAME") %>'></asp:Label><asp:TextBox ID="MATNAME" runat="server" Text='<%# Eval("MATNAME") %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Received Date"><ItemTemplate><asp:Label ID="ReceivedDateLabel" runat="server" Text='<%# Eval("SAMPDATE") %>'></asp:Label><asp:TextBox ID="ReceivedDate" runat="server" Text='<%# Eval("SAMPDATE") %>' Width="175px" visible="false"></asp:TextBox><asp:CalendarExtender ID="ReceivedDateExtender"  TargetControlID="ReceivedDate"  runat="server"  Format="dd/MM/yyyy"  ></asp:CalendarExtender></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="QA Due Date"><ItemTemplate><asp:Label ID="QADueDateLabel" runat="server" Text='<%# Eval("SAMPDATE") %>'></asp:Label><asp:TextBox ID="QADueDate" runat="server" Text='<%# Eval("SAMPDATE") %>' Width="175px" visible="false"></asp:TextBox><asp:CalendarExtender ID="QADueDateExtender"  TargetControlID="QADueDate"  runat="server"  Format="dd/MM/yyyy" ></asp:CalendarExtender></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Physical Testing" ItemStyle-Width="40" ItemStyle-HorizontalAlign="Right" ><ItemTemplate><asp:Label ID="PhysicalTestingLabel" runat="server" Text='<%# Eval("physicalTestComplete") & "/" & Eval("physicalTotal")  %>'></asp:Label><asp:PopupControlExtender 
                    ID="PopupControlExtender1"
                    runat="server"
                    TargetControlID="PhysicalTestingLabel"
                    PopupControlID="Pnl_TestExtender"
                    DynamicContextKey='<%# Eval("MATCODE") %>' 
                    DynamicControlID="Pnl_TestExtender" 
                    DynamicServiceMethod="GetDynamicContent" ></asp:PopupControlExtender ></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Name" ><ItemTemplate><asp:Label ID="PhysicalTestingNameLabel" runat="server" Text='<%# Eval("ORIGREC") %>'></asp:Label><asp:TextBox ID="PhysicalTestingName" runat="server" Text='<%# Eval("ORIGREC") %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Instrumentation Testing"  ><ItemTemplate><asp:Label ID="InstrumentationTestingLabel" runat="server" Text='<%# Eval("instrumentationTestComplete") & "/" & Eval("instrumentationTotal")  %>'></asp:Label><asp:TextBox ID="InstrumentationTesting" runat="server" Text='<%# Eval("instrumentationTestComplete") & "/" & Eval("instrumentationTotal")  %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Name" ><ItemTemplate><asp:Label ID="InstrumentationTestingNameLabel" runat="server" Text='<%# Eval("ORIGREC") %>'></asp:Label><asp:TextBox ID="InstrumentationTestingName" runat="server" Text='<%# Eval("ORIGREC") %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Microbiology"  ><ItemTemplate><asp:Label ID="MicrobiologyTestingLabel" runat="server" Text='<%# Eval("microbiologyTestComplete") & "/" & Eval("microbiologyTotal")  %>'></asp:Label><asp:TextBox ID="MicrobiologyTesting" runat="server" Text='<%# Eval("microbiologyTestComplete") & "/" & Eval("microbiologyTotal")  %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Name" ><ItemTemplate><asp:Label ID="MicrobiologyTestingNameLabel" runat="server" Text='<%# Eval("ORIGREC") %>'></asp:Label><asp:TextBox ID="MicrobiologyTestingName" runat="server" Text='<%# Eval("ORIGREC") %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Other"  ><ItemTemplate><asp:Label ID="OtherTestingLabel" runat="server" Text='<%# Eval("otherTestComplete") & "/" & Eval("otherTotal")  %>'></asp:Label><asp:TextBox ID="OtherTesting" runat="server" Text='<%# Eval("otherTestComplete") & "/" & Eval("otherTotal")  %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Name" ><ItemTemplate><asp:Label ID="OtherTestingNameLabel" runat="server" Text='<%# Eval("ORIGREC") %>'></asp:Label><asp:TextBox ID="OtherTestingName" runat="server" Text='<%# Eval("ORIGREC") %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Reviewed"  ><ItemTemplate><asp:Label ID="ReviewedLabel" runat="server" Text='<%# Eval("ReviewedComplete") & "/" & Eval("ReviewedTotal")  %>'></asp:Label><asp:TextBox ID="Reviewed" runat="server" Text='<%# Eval("ReviewedComplete") & "/" & Eval("ReviewedTotal")  %>' Width="175px" visible="false"></asp:TextBox></ItemTemplate></asp:TemplateField></Columns></asp:GridView><asp:Panel ID="Pnl_TestExtender" runat="server" >       </asp:Panel></asp:Content>

And my code behind:

 Protected Sub Gvw_Batches__RowCreated(sender As Object, e As GridViewRowEventArgs)
        If e.Row.RowType = DataControlRowType.DataRow Then
            Dim pce As PopupControlExtender = TryCast(e.Row.FindControl("PopupControlExtender1"), PopupControlExtender)

            Dim behaviorID As String = "pce_" + e.Row.RowIndex.ToString
            pce.BehaviorID = behaviorID

            Dim lbl As Label = DirectCast(e.Row.FindControl("PhysicalTestingLabel"), Label)

            Dim OnMouseOverScript As String = String.Format("$find('{0}').showPopup();", behaviorID)
            Dim OnMouseOutScript As String = String.Format("$find('{0}').hidePopup();", behaviorID)

            lbl.Attributes.Add("onmouseover", OnMouseOverScript)
            lbl.Attributes.Add("onmouseout", OnMouseOutScript)
        End If
    End Sub<System.Web.Services.WebMethodAttribute(), System.Web.Script.Services.ScriptMethodAttribute()> _
    Public Shared Function GetDynamicContent(contextKey As String) As String

        Dim b As New StringBuilder()
      

        Dim rowing = GenerateTestBatchTable(contextKey)
        For Each row In rowing




            b.Append("<table style='background-color:#f3f3f3; border: #336699 3px solid; ")
            b.Append("width:350px; font-size:10pt; font-family:Verdana;' cellspacing='0' cellpadding='3'>")

            b.Append("<tr><td colspan='3' style='background-color:#336699; color:white;'>")
            b.Append("<b>Product Details</b>")
            b.Append("</td></tr>")
            b.Append("<tr><td style='width:80px;'><b>Unit Price</b></td>")
            b.Append("<td style='width:80px;'><b>Stock</b></td>")
            b.Append("<td><b>Description</b></td></tr>")

            b.Append("<tr>")
            b.Append("<td>$" + row("'<%# Eval(""Analyte"") %>'").ToString() + "</td>")
            b.Append("</tr>")

            b.Append("</table>")
        Next

        Return b.ToString()
    End Function

Thank you for your help