I have had the same experience with Excel 2010. Everything was working fine until about three weeks ago then, for no apparent reason, though I'm sure there is one, the error message apeared and I have been unable to save Excel files as PDF since. I also used Norton 360 until a few days ago when I uninstalled it and activated Microsoft Security Essentials and Microsofts Firewall instead. The problem remains the same. Still unable to save as PDF or XPS.