There were 3 times this happened to me. The first corrected itself when I changed the file name (no hyphens, etc.); the second had something to do with obscure fonts that were either missing or corrupted on the PC side (although that once happened to me as well, and I had to re-install PP); the third didn't like the fact that it couldn't find a QT file in the presentation so it just refused to open anything else.