It seems that you have hit the 5 GB disk space usage for your account, which is probably why you’re experiencing problems managing files.
However, the thing you should do then is to delete files, which means that deleting files should work. But it appears that something is not working right and making you unable to delete these files.
I’m not sure if the underlying problem was resolved (I don’t think it is, it’s a bug in the underlying quota system, which is hard for us to fix), but the directory in question has been removed now.
I completely agree. But from what I understand, it’s a bug deep inside the operating system of the server, which goes much deeper than the kind of issues we can typically fix. So it’s hard to actually fix this.