Running out of space???

I just tried to download a small image and I get this message: "Cannot finish download. There is not enough space". Problem is that I am not running out of space. When I go to SD and phone storage it says:

Internal SD card:

total space: 13.43 GB
Available space: 12.68 GB

(I don't have an external SD card, FWIW).

So what is going on here? I'm not rooted BTW.