Subfolder creation not working

I have been given Manager status for a project. When I try to create a Subfolder, the creation dialogue box pops up, but when I click the CREATE button, nothing happens. I've tried in three different browsers. In Chrome, the button doesn't even seem to operate; in Firefox and IE 11, the button seems to operate but the dialogue box just stays on screen and nothing happens.

Is there a browser setting I need to change?