On occasions, you may encounter problems opening PDFs. The reason for this to happen is most likely due to the time out error. This could be due to a slow internet connection or a large download size. Many times, articles with images contained in them will time out the download.
To resolve this, right click on the link "Proceed to PDF" and select "Save Target As..." (or "Save Link as..." for Firefox). This will allow you to save the PDF to your computer and should allow for a faster, more successful download.