There is no problem with web.config. Your web site runs under a process. In iis you can define the identity of that process. The identity that, your web site’s application pool runs as (Network Services, Local System, Etc. …), should have permission to access and read web.config file.
This problems occurs because your application can not access and read web.config file.
Make the file accessible to IIS_IUSRS group. Just right click web.config and click properties, under security tab, add IIS_IUSRS.
So what is this IIS_IUSRS?
Your web site is like an exe file. Just like any exe file, it should be started by a user and it runs according to permissions assigned to that user.
When your site is started in IIS, Application Pool of your web site is associated with a user (Network Services, Local System, Etc. …) (and can be changed in IIS)
So when you say IIS_IUSRS, it means any user (Network Services, Local System, Etc. …) that your site is running as.
If your computer is on a domain, remember that IIS_IUSRS group is a local group.i
If still the problem persists then make the web config file accessible to user group “Users” as well.
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