Are the error messages coming up in the correct application? i.e. when you double click an .ai file is it actually Illustrator that is supplying the error message or could it be another app? I ask because it is possible that Windows XP is defaulting to another program to try to open your file and can't so produces the error. If that's the case, reset Windows to open .ai files in Illustrator.

Hope that helps,

Michael

http://www.learnadobesoftware.com

From post 15 of this threaad:

http://forums.adobe.com/message/3899466#3899466

"I'll add an update to this problem using a Windows 7 Toshiba laptop running CS6 - I began to recieve the same message and Illustrator would resize itself to 1"h x 5"w box in the upper left of my screen.  Illustrator itself would be hidden behind the error dialogue box.

This would happen when I'd select an Illustrator file in Windows Explorer.  The first workaround was to maximize Illustrator and open the file through the Illustrator File>Open dialogue.  This always worked.

The final fix was to manually resized illustrator to about 1/3 screen size and try to open the file again in Windows Explorer.  Finally the files would open from Windows Explorer.  Keep reading.

However, each time I opened a file Illustrator would do a little hula dance and resize a good bit smaller than what I'd manually set it to.  It took about 4 resizes and 4 opening of files  = each time resizing the illustrator window larger until it actually occupied the whole screen.  It's working normally now."

Also, what happens if you open Illustrator and use File > Open?

--OB

Edit to add: There are other suggestions in that thread as well. Also several other threads dealing with the same subject if you search on  the error message you are getting. <OB>

This still sounds a bit like the windows directory that says what app opens which filetype is out of whack. To fix your Acrobat problem, you can tell acrobat to open object art in Illustrator via Acrobat's preferences.

here's a screen capture of Acrobat's preference indow:

Hope that helps a bit,

Michael

http://www.learnadobesoftware.com