I have this issue with my PRS-T1 also. If I were to hazard a guess I would think maybe it's because the file is written using a later version of Acrobat. I know that at work some pdfs won't work properly unless the computer is updated to Acrobat XI.
I don't know that there is any solution other than converting it to an epub.
Last edited by luvduchovny; 01-15-2013 at 05:57 PM.