Most of this problem occurs because of permission issues. There are many solutions online. I will only talk about the problems I encountered
As shown in the picture
In the afternoon, a colleague told me that the company website cannot be accessed. After checking the records, I found that the system directory permissions were set when I logged in today. First of all, it is definitely not a problem with IIS. The website directory permissions are correct. I also found that 2 of the company's four websites can be opened, but they cannot be opened by ASP scripts. The 2 websites cannot be opened by PHP scripts. The problem is obvious. It is obvious that the website cannot call the PHP program. Go to the PHP installation directory and set permission attributes - safely add user read permissions. Problem solved.