How do I open PS4 without having to delete my preferences?

Question

I have been using CS3 Web Prem, but just updated to CS4 Web Prem.  I installed the suite, registered, downloaded all updates, and downloaded the most recent driver for my graphics card (GeForce 9800T).  I have 4 GB RAM and use Vista Home Premium for the OS.  I have not had any problem using PS3 and Lightroom 2.3.  (CS3 is still on the computer.)
When I first opened Photoshop CS4, I changed the scratch disk in my preferences and closed the program.  The next time I tried to open PS, it wouldn't open.  Instead I got two dialog boxes saying that the scratch file and activation files were locked and telling me to use Windows Explorer to unlock them.  I then opened PS while holding down the alt-contr-shift keys and changed the preferences back the way they originally were, with the C drive as the scratch drive under the Performance tab.  I closed PS and tried to reopen it again.  The same warnings about the scratch and activation files appeared. I do not know where to find the scratch and activation files, and the only way I can open PS is by deleting the Preferences. 
What do I need to do in order to set the Preferences, save the changes, and open PS without having to delete the new Preferences?
Thank you for your assistance.

Answer 1

It is likely to be due to the intervention of the UAC on Vista. Turn it off and see if the problem goes away.
I turned it off when I got Vista and left it off.
If you want to keep it you will have to run the program as Administrator I guess.