Notes from the field: if you forget to install IIS application development support for your ASP.NET application, IIS will complain about a locked configuration section

Today's blog post is a quick solution to a real-world problem: you are deploying your ASP.NET web application to a new Windows server with IIS installed. You diligently copy your files to a virtual application folder, and then launch your web browser. Everything looks good until you get an IIS error message 500 about locked configuration sections.

Of course, there are many different reasons why this particular error might occur, but here's one more: if you by mistake happen to forget to actually install ASP.NET application support to your IIS server, you will run into the mentioned error message. By looking at the error message alone, you simply can't know about the real reason.

But in my case, the solution was simple: make sure application development support features are installed to your server. It is not enough to install .NET 4.x using Windows Server's Server Manager "Add Roles and Features" command, because you specifically have to install application development support features, too.

One you have installed these features, the locked configuration section error magically goes away, and your application suddenly works.

Problem solved!