PDF files opening with blank pages on a Mac OS X computer, what should I do?
First download the files onto your desktop. If you hold the Option button down while clicking on the file it will download. Once downloaded select one file. Go to the menu and click on File, Get Info. Under Open with: choose Acrobat reader. Click the Change All button under Use this application to open all documents like this. Now whenever you get a PDF file it will open with the Acrobat reader. 39. I get “Challenge Token Null” error when I try to log into Blackboard. This is usually caused by book marking the logon page instead of the Blackboard entry page. You need to start your blackboard session at http://blackboard.dickinson.edu click the “Login” button on that page. When you do that, Blackboard then opens the logon screen and begins what is called a “session” that will permit you to log in without the “Challenge Token Null” error.
