This application is currently offline. To enable the application, remove the app_offline.htm file from ...

出现此问题时：

This application is currently offline. To enable the application, remove the app_offline.htm file from the application root directory

原因是应用程序脱机。

解决的办法是：找到你的程序的根目录，把app_online.html文件删掉即可。