From Adobe Illustrator CS6:

While it’s possible that Adobe has a codified error database for “CANT” … it would seem more likely that someone will need to search through source code to find out what operation cannot complete.

(To fix the above problem, I reset the settings for Illustrator by running as admin and holding down CTRL+SHIFT+ALT. Illustrator starts in a weird mostly not working state, but after shutting down that instance and restarting normally, the error went away).

This one is slightly better:

Although, in a clean install of CS6, I don’t know why I’m getting this error.

Photoshop upon first run was giving me an error message:

Could not open a scratch file because the file is locked, you do not have necessary access permissions, or another program is using the file. Use the "Properties" command in the Windows Explorer to unlock the file.

You’ll note that it mentions a file being locked, but no clear action to take because of this issue.

Here’s what apparently is one cause of this error:

A non-default installation of Windows (or Macs), where your temporary and user folders are not on the installation disk for Photoshop. In my case, I have 3 disks in my computer:

1. SSD  < Apps installed
2. 600GB HD  < Users, temporary
3. 600GB HD < Virtual Machines, backups, etc.

Photoshop (and Illustrator as well actually) try to create the scratch folder on the primary drive, even when they don’t have permission to do so. I changed the setting by:

1. Run Photoshop as Administrator
2. Immediately hold CTRL+ALT+SHIFT.
3. Photoshop will ask if the Settings should be reset. Answer OK.
4. Go to Edit > Preferences > Performance
5. Make changes to Scratch Disks:
   
6. Click OK and Exit Photoshop
7. Restart normally.