I think that PDF file is just not compatible with adobe Ver 5 (I run ver 5 because I have the Pro Ver that lets me create and edit PDFs), because I can open the same PDF on a different PC running adobe Ver 7.
I use to be able to open the 1.2 RC2 PDF with adobe Ver 5, something must have changed in the creation of the RC4 PDF that makes it not as compatible with older/other PDF readers.
It is not a major problem, On my other PC I can re-save the PDF to a readable format for Adobe Ver 5. I just thought you might want to be aware when the next PDF is created.