I was in the RoboHelp 7 Project Manager pod. The HTML Files (Topics) folder was highlighted. I right-clicked and selected New > Folder.
This is perfectly normal. You need to understand that the Project Manager is simply RoboHelp's way of organizing the different project assets. Think of it as perhaps "filters" that are only showing you files that are used. For example, when you look at the files and folders of the project in Windows Explorer, you will never see a folder named "Baggage Files" or "Style Sheets". And if you create a folder, even though you see it in Baggage Files, Images, Cascading Style Sheets and HTML Topics, it's only on your hard drive once.
Hopefully this helps... Rick