Tried to download the file from http://www.malot.fr/bootstrap-datetimepicker/ and added the files datatimepicker.min.css and datatimepicker.js
<div class="col-sm-3 col-lg-2 input-group date">
<%--<asp:Calendar runat="server" CssClass="form-control" ID="calender"></asp:Calendar>--%>
<asp:TextBox runat="server" CssClass="form_date" data-date-format="dd MM yyyy" ID="fromdate" AutoPostBack="true" OnTextChanged="fromdate_TextChanged" ></asp:TextBox>
<asp:Label ID="lbldateerror" BackColor="Red" runat="server"></asp:Label>
</div>