http://kb2.adobe.com/cps/332/332690.html Error "An unknown error has occurred" when you save an Illustrator CS2 file (Windows XP) Issue When you choose to save an Adobe Illustrator file as an AI or PDF file, the application returns the error message, "An unknown error has occurred." Solutions Do one or more of the following solutions: Solution 1: Re-create the Transparency Flattner Presets file..