Server application unavailable Solution

Error message:

Server application unavailable
The Web application you are attempting to access on this web server is currently unavailable. Please hit the "refresh" button in your web browser to retry your request.

Administrator Note: an error message detailing the cause of this specific request failure can be found in the application event log of the Web server. please review this log entry to discover what caused this error to occur.

Solution:

ApplyProgramAdd iis_wpg to the directory

Open my computer -- [tools] -- [Folder Options] -- [view]
Now we can see [advanced settings]. Find [use simple file sharing (recommended)], remove the check mark before it, and then open the folder properties to see, you can add the iis_wpg permission to the Security tab.