Many times when a web app won't run, it's the simple things like setting an Application Identifier that are causing the trouble. Your web application must have an Application Identifier specified on the App properties or the web application will not start.
The Application Identifier can be set in three simple steps:
1. Click on the Project tab
2. Select the App class
3. Edit the Application Identifier property
The format usually looks like this:
You can find more details on the Application Identifier at our Documentation Wiki: