The .DS_Store file can be deleted while booted in OS 9. The one you want to delete is in /Users/Sam's Home directory/Desktop
or use the Terminal either as the admin:
rm /Users/Sam/Desktop/.DS_Store
or login as Sam:
cd Desktop
rm .DS_Store
The cache to remove may be this one...but I'm guessing:
com.apple.LaunchServices.UserCache.csstoreHow do you feel about my guesses?
I'd use Jaguar Cache Cleaner and do a
light cleaning.
Remember, I don't know what's causing the message to keep appearing...all this may be in vain.