PDF files will not open in IE, Firefox, and Safari. This started with 4.2.2 and the latest version of WP-Filebase.
Sometimes you get error stating network connection error and sometimes not. Changing the "Enable Protection On" in the PDF readers does not resolve. It also alternates whether it will open the file. You may be able to open the file at one moment, but open another file or switch pages and then come back to that link and it will not open the file that you could previously open.
Temporary fix: I had to upload all my PDF files into the Media Library and add them to the page; removing the wp-filebase code. NO ISSUES now.