I am having the same issue. I downloaded two vectors yesterday, then got that same popup window. So I just tried again (a full 24-hours after my last download yesterday) and I'm still getting that message.
This is the first time I've run into this EVER, and some days I download a lot of little teeny vectors to edit and add shapes and textures to larger projects I'm working on. There have been days when I've downloaded over 15 images and never got that pop-up.
It would be nice if they would tell us our daily limit, or just tell us that our All Apps subscription no longer includes ANY free images/vectors/art of any kind.