I got a report from one of my readers (thank you!) about error messages delivered when trying to download PDF files from Box.net.
It turned out Box.net had changed all the settings in my account. I have reset them now, and hopefully the links will work correctly now.
By the way: I have built in some redundancy in the system as you may download the files from Divshare as well as Box.net. If both of them should fail, you may even download the PDF from Slideshare.