I host several different WordPress sites on my hosted shared server.
All have now developed this error when trying to upload images or PDF files. They can't be moved to the wp-content/uploads/..... folder.
I was last able to upload some images on 18th October, but today I'm presented with this "cannot be moved" error.
I've not changed anything on the server. I'm running v3.5.2 and v3.6.1 so the problem is not linked to a specific version.