can some one help me where I went wrong in the following code

<asp:GridView ID="grdnewUser" runat="server" AutoGenerateColumns="false" GridLines="None">
                                            <Columns>
                                                <asp:TemplateField>
                                                    <ItemTemplate>
                                                        <ul class="last_post">
                                                            <li>
                                                                <asp:Label ID="lblDateposted" Text='<%#Eval("DatePosted") %>' Font-Underline="false"
                                                                    runat="server"></asp:Label>
                                                            </li>
                                                            <li><strong>In:</strong>
                                                                <asp:Label ID="Label1" Text='<%#Eval("QuestionTitle") %>' Font-Underline="false"
                                                                    runat="server"></asp:Label>
                                                            </li>
                                                            <li><strong>By:</strong>
                                                                <asp:LinkButton ID="lnkUsername" runat="server" Text='<%#Eval("UserName") %>' Font-Underline="false"></asp:LinkButton>
                                                            </li>
                                                        </ul>
                                                    </ItemTemplate>
                                                </asp:TemplateField>
                                            </Columns>
                                        </asp:GridView>

public void bindLastPost()
        {
            ArrayList a = new ArrayList();

            foreach (GridViewRow row in grdForum.Rows)
            {
                int quesID = Convert.ToInt16(grdForum.DataKeys[row.RowIndex].Values["TechID"].ToString());
                var lastpost = db.tblQuestions.Where(u => u.TechID.Equals(quesID)).OrderByDescending(u => u.DatePosted).Take(1).FirstOrDefault();

                a.Add(new Results { DatePosted = lastpost.DatePosted, QuestionTitle = lastpost.QuestionTitle, UserName = lastpost.UserName });
            }

            var query = from Results student in a
                        select student;
            grdnewUser.DataSource = query.ToList();
            grdnewUser.DataBind();
}

DataBinding: 'ForumsApp.Main1+Results' does not contain a property with the name 'DatePosted'.