ASP.NET

public override void Install(System.Collections.IDictionary stateSaver)
        {
            base.Install(stateSaver);

            String MyServer = Context.Parameters["MyServer"];
                        
            String server = "Username=sa;Password=wow;Database=OBooking_Master;Server=" + MyServer;

            String Key = "TESTY";

            UpdateConfig(Key, server);


        }


        public void UpdateConfig(string strKey, string strValue)
        {

            Configuration objConfig = WebConfigurationManager.OpenWebConfiguration("~");

            AppSettingsSection objAppsettings = (AppSettingsSection)objConfig.GetSection("appSettings");

            if (objAppsettings != null)
            {

                objAppsettings.Settings[strKey].Value = strValue;

                objConfig.Save();

            }
        }

The Application relative Virtual path '~' is not allowed here 

Configuration objConfig = WebConfigurationManager.OpenWebConfiguration(HttpRuntime.AppDomainAppVirtualPath);

Object reference not set to an instance of an object 

Configuration objConfig = WebConfigurationManager.OpenWebConfiguration(@"~\Install_Helloworld\Web.Config");

/MyServer="[EDITA1]\"

<ajaxToolkit:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="addComment_lnk"
                BackgroundCssClass="modalBackground" PopupControlID="Panel1">
            </ajaxToolkit:ModalPopupExtender>
            <asp:LinkButton ID="btn_hide" runat="server"></asp:LinkButton>
            <asp:Panel ID="Panel1" CssClass="popBox" runat="server" Style="display: none">
                <div>
                    <p style="text-align: center">
                        <table>
                            <tr>
                                <td class="title">
                                    Post Comment :
                                </td>
                            </tr>
                            <tr>
                                <td>
                                    <asp:TextBox ID="comments_txt" CssClass="popInput" TextMode="MultiLine" runat="server"></asp:TextBox>
                                </td>
                            </tr>
                            <tr>
                                <td>
                                    <asp:Button ID="post_btn" CssClass="button buttonGreen floatRight" OnClick="post_btn_Click"
                                        runat="server" Text="Post" />
                                    <asp:Button ID="cancel_btn" CssClass="button buttonGray floatRight" runat="server"
                                        Text="Cancel" />
                                </td>
                            </tr>
                        </table>
                    </p>
                </div>
            </asp:Panel>
<asp:LinkButton ID="addComment_lnk" runat="server">Add Comment</asp:LinkButton>

protected void btnSave_onClick(object sender, EventArgs e)
{
foreach (GridViewRow row in Control.GridViewRows)
{
CheckBox cboxremove = (CheckBox)row.FindControl("cbxRemove");
if (cboxremove.Checked)
{
RemoveCheckedTitles();
}
else 
{ 
???????????????
}
}