Cannot open in Viewer

I created a presentation in PowerPoint 2007 and I wanted to have it printed
at a shop so they installed PP Viewer 2007, but couldn't open the file. They
get the following error: PowerPoint Viewer cannot open the file
"filename.pptx".

To make sure it wasn't their problem I installed PowerPoint Viewer 2007 on
another one of my computers, but I got the same error. In the end I just
saved it as a PDF, but all the bevelled fonts looked terrible.

For future reference does anyone know how to fix this? I want to either be
able to open the .pptx file in viewer 2007 or save it as a pdf so the
bevelled fonts are sharp.

Thanks,
Lawrence

PS. I also saved it as *.ppt file and viewer 2007 was able to open it, but
somethings were not right, such as the bullet point symbols.