I have a free account, which I'm playing with (full disclosure: I had another free account previously which I barely used, but I'm getting back into coding).
I tried to create a new file in the Files tab. When I move the cursor over the New File button, the "hand" cursor has a red "no entry" image over it, and clicking the button does nothing. The same happens when I try to click "New Directory".
This first happened while I was in the tarpit, so I assumed it might be that. I had previously created a couple of files, and I thought maybe a free account had a limit, so I deleted them - but I still have the problem.
If it's relevant, I'm accessing the site via Chrome on a Chromebook.