Since the last 2015 update, the vector graphics (in PDF form) in my documents are showing up as gray boxes with x's over them, especially when I am in Overprint Preview. This hasn't happened before. I am using a Macbook Pro. This was an issue both with Yosemite OS as well as the recent El Capitan upgrade. What can I do so that I can see my graphics when working in a document in either Typical or Overprint Preview mode?