How do I fix the “compilerVersion” IIS error?

Question

I\'m getting this exception:

System.Configuration.ConfigurationErrorsException: The value for the \'compilerVersion\' attribute in the provider opti

Answer 1

We had accidentally copy-pasted Web.config into C:\inetpub\wwwroot. This accidentally copy-pasted Web.config had mismatching configuration and caused the compilerVersion error for us. Deleting the Web.config solved the problem for us.