OK, guys, I think this is going to be very helpful for some people. I've been struggling for days and nights trying to solve the problem of not being able to save my AIs as PDFs.
At the beginning, when I had just bought and installed the Adobe Creative Suite 2, everything was running smoothly. I was able to convert any type of files (Excel, Word, Powerpoint...) to PDF. But suddenly, the Adobe automatic updater advised me of some new Acrobat Professional changes. I accepted them and something I haven't heard about before, appeared on my applications software tool bars: FLASH PAPER2. From then on, I wasn't able to convert my documents using just one button. Every time I tried it my application program hanged up. Now I had to work around by printing it to the PDF Adobe Printer. Well, that at least solved that problem.
Later, working with AI (CS2) I noticed that I couldn't save some AI documents as PDF any more. Then I started looking and looking for a solution, until I finally found this thread. The answer wasn't here at all. I tried several suggestions, but none worked for me. So I decided to re install Adobe Illustrator and Adobe Acrobat and the problem disappeared.
I'm almost sure that one of the automatic updates that I allowed to be applied to my CS2 suite caused the error.
Sorry for such a long story.
Virgilio