I've looked on the Adobe site and I've spoken to the web designer. The web man has confirmed there isn't anything wrong with the server or the PDF.
Here are two things which he (and Adobe) suggest:
Problem with the PDF?
Refresh or reload the page
Often, just refreshing the page allows the PDF to fully load.
•Hold down the Shift key and press the Refresh or Reload button in the browser. (I use F5 or shift F5).
Go to the Newsletter page of the website vasculitis.org.uk/about/new...
and RIGHT click on the blue link for the Spring 2013 Newsletter, and then save the file. Then you should be able to view it in Adobe Reader rather than on your browser.
Perhaps you could send me an e-mail to say whether either of these have worked for you: firstname.lastname@example.org Many thanks.