Can I assume you're working with Illustrator 9.0.x? The error message: "ARTONPATH.AIP does not exist in the expected location and cannot be updated.” This is a required file for the Adobe Illustrator 9.0.2 update. Find the files ArtOnPath.aip & Scatter Brush Tool.aip, notice the capitalization and spacing for these two files. Name them exactly.
I recommend you do a complete, clean re-install of the application and any upgrades. Simply re-installing or even un-installing and re-installing may not be sufficient. First off, use Windows add-remove programs, then check for any left-over files or folders and remove those. Then remove any .TMP files on your drive(s) and do a disk de-frag. Then shut your computer down. When you re-start do so in safe or VGA mode -- or at least make sure no TSRs start. (like virus scans or screen savers) Use Control –Alt-Delete to bring up TASK LIST, then one by one, END TASK everything on the list except Explorer and Systray. Then do a complete install as administrator from the original CD-ROM from Adobe and then any upgrades.
I've moved your other Topic to join this one already in progress since they both deal with installation issues, I believe. Let me know if a clean re-install works for you ...
Do a Control F, then in the options be sure to check SHOW HIDDED FOLDERS/FILES, the type in AIPrefs, including your operating system drive (usually C:) to look in. This should show you where your AIPrefs file is, but you can Delete it directly from here and that'll work too.
Bob
Have you tried Save As? Do those filenames or paths include extended characters? Try saving to C:\TEMP\TEST.AI as a test. What exact version of Illustrator X.X.X are you using? There were save problems which were fixed by patches to 9.0.2 and 10.0.3 available from Adobe downloads.