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

In my case it was a child site under the Default Website and although the default website settings were set at ASP.NET 4.0, the web.config file was set for 2.0 and 3.5. Changing the web.config file to use 4.0 fixed it. Use this for reference: ASP.NET 4 Breaking Changes