ajax autocompleteextender not working

Hello and thanks for reading this.

Im trying to use the ajax autocompleteextender. I have installed ajax using the Manage NuGet system in VS13

I have connect everything according to guides but the events dont work at all.

ASP:<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server" EnablePageMethods="true" /><asp:TextBox runat="server" ID="txtIntervalStudent" /><asp:AutoCompleteExtender runat="server" ID="aceIntervalStudent" ServiceMethod="SearchStudent"
                            TargetControlID="txtIntervalStudent"
                            MinimumPrefixLength="1"
                            CompletionInterval="1000"
                            CompletionSetCount="20"
                            EnableCaching="true" 
                            FirstRowSelected="false" />

C#:

[System.Web.Script.Services.ScriptMethod()]
    [System.Web.Services.WebMethod]
    public static List<string> SearchStudent(string prefixText, int count)
    {
        using (SqlConnection conn = new SqlConnection("Data Source=PCM13812;Initial Catalog=KONE;Persist Security Info=True;User ID=sa;Password=c03041988;MultipleActiveResultSets=True;Application Name=EntityFramework"))
        {
            using (SqlCommand cmd = new SqlCommand())
            {
                cmd.CommandText = "SELECT Username FROM [Users] where" + "Username like @Searchtext + '%'";
                cmd.Parameters.AddWithValue("@Searchtext", prefixText);
                cmd.Connection = conn;
                conn.Open();
                List<string> names = new List<string>();
                using (SqlDataReader sdr = cmd.ExecuteReader())
                {
                    while (sdr.Read())
                    {
                        names.Add(sdr["Username"].ToString());
                    }
                }
                conn.Close();
                return names;
            }
        }
    }

What could be the problem?

Thanks alot