ASP.Net Error: Cannot create an object of type System.Int32 from its string representation '' for the RepeatColumns property

unable to see the design on the page in asp.net c#

Cannot create an object of type 'System.Int32' from its string representation '' for the 'RepeatColumns' property

            <div class="row">
                <div class="col-md-12">
                    <div class="table-responsive">
                        <asp:DataList ID="DataList1" runat="server" RepeatColumns="" RepeatLayout="Flow">
                            <HeaderTemplate>
                                <table class="table table-border table-striped custom-table datatable mb-0">
                                    <thead>
                                        <tr>
                                            <th>Name</th>
                                            <th>Age</th>
                                            <th>Address</th>
                                            <th>Phone</th>
                                            <th>Email</th>
                                            <th class="text-right">Action</th>
                                        </tr>
                                    </thead>
                            </HeaderTemplate>
                            <ItemTemplate>
                                <tbody>
                                    <tr>
                                        <td>
                                            <img width="28" height="28" src="../assets/img/user.jpg" class="rounded-circle m-r-5" alt="">
                                            Jennifer Robinson</td>
                                        <td>35</td>
                                        <td>1545 Dorsey Ln NE, Leland, NC, 28451</td>
                                        <td>(207) 808 8863</td>
                                        <td><a href="http://dreamguys.co.in/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="adc7c8c3c3c4cbc8dfdfc2cfc4c3dec2c3edc8d5ccc0ddc1c883cec2c0">[email&#160;protected]</a></td>
                                        <td class="text-right">
                                            <div class="dropdown dropdown-action">
                                                <a href="#" class="action-icon dropdown-toggle" data-toggle="dropdown" aria-expanded="false"><i class="fa fa-ellipsis-v"></i></a>
                                                <div class="dropdown-menu dropdown-menu-right">
                                                    <a class="dropdown-item" href='<%=ResolveUrl("~/Edit-Patient")%>'><i class="fa fa-pencil m-r-5"></i>Edit</a>
                                                    <a class="dropdown-item" href="#" data-toggle="modal" data-target="#delete_patient"><i class="fa fa-trash-o m-r-5"></i>Delete</a>
                                                </div>
                                            </div>
                                        </td>
                                    </tr>
                                    
                                </tbody>
                            </ItemTemplate>
                            <FooterTemplate>
                                </table>
                            </FooterTemplate>
                        </asp:DataList>
                    </div>
                </div>
            </div>

in design mode is viewable but while run the page to browser that time unable to seen design

we have try to another pc and VS2010 still faccing the same issue