It sounds like you copied the files from old drive to new drive. While this may work you might have better luck if you installed the program on the new drive with disks. In PS there are a number of files that are "common files" that have to be in a certain place on the main drive for program to work well. If you just copied everything over this might upset the balance.
1. I didn't replace the boot drive, which is where all the application software is/runs from. Files were migrated from the boot to the new 1TB *backup* drive.
2. As I said, I did reinstall Photoshop from scratch, thinking that it needed to 'learn' the new drive setup before it would allow scratch disk setup.
3. I don't ever move system or application files from where an installer places them.
Update - I just purchased the release of Photoshop CS6 (Extended); uninstalled the public beta; installed the purchased product.
Photoshop still won't recognize either of my backup drives as scratch disks.
Have you reset your preferences? Click on start icon for Photoshop and IMMEDIATELEY hold down the CMD + OPTION + SHIFT keys. A little tricky but you should get a reset window. If you see splash screen you are too late.
Does you OS see all 3 drives? Might need a Mac guy to weigh in.
I'm using Windows here, but I have experienced drives becoming read only when adding drives, and I have seen other reports of similar problems.
Please read my original post (bullet item 6).
General comment - if you aren't going to give the original, detailed description a focused reading, then please don't post a reply. I haven't got the time to answer answered questions.
Also - no bragging intended - I am a Mac guy. I know the platform well, so anyone who wants to offer a Mac-related observation can assume I know what I'm doing and talk on an advanced level.
One additional observation - the problem persists when logged in under a different user account.
I still have this problem.
Sometime next week, I'm going to install an older, "non-Lion" 300gb drive in my 4th drive bay, just to see if Photoshop/Illustrator will accept that drive as a scratch disk.
I'm still thinking this has something to do with installing a new drive & formatting it for use as a Lion-compatible volume (i.e. as Mac OS Extended with a recovery partition).
I can confirm that the "non-Lion" 300 gb drive can be selected and used as a scratch disk by both Photoshop (CS5 & 6) and Illustrator (CS5). Since all 4 of my drives (the 3 1TB's, and the 300) were base formatted the same, the evidence is pointing to this problem having something to do with the fact that the 1TB's are clones of the Lion boot drive (the 300 is blank at this point - no Lion recovery partition or OS files).
I'd really appreciate it if one of the Adobe engineers who monitors the forums could speak up at this point. The whole point of having 4 drive bays is to be able to facilitate disk-related functions such as scratch disks, so I'd like to get some help figuring out why I'm having this problem with Photoshop and Illustrator.