Form not visible in task bar
When you support old code, you get a lot of surprises and you learn a lot of things. I had a client tell me that one of the forms windows written in Visual Studio with C# needed its own window. I didn't understand what he meant. He kept saying that when he switched between apps, he couldn't find a certain form on the C# app. When pressed further as to the problem, it turned out that when he hovered over the app in the task bar, if he had different forms open, one was not visible in the task bar. This required some investigation.
As it turns out, there is a Form property which is a boolean. It is called Form.ShowInTaskbar.
So when I added the following line to the constructor, everything was fixed:
this.ShowInTaskbar = true;
I still don't know what was turning it off, but the explicit assignment fixed the problem.
Hope this helps someone.