Somehow I cannot delete RAW files that I shot with the S3 IS. I tried different firmware versions, but its the same for all of them. The only way is to either format the card (and lose the firmware settings) or to boot the computer in Safe mode where I can delete the files. Oddly enough, when I copy the files to my computer, I also cannot delete them.
I get a message: "Cannot delete CRW_xxxx:It is being used by another person or program. Close any programs that might be using the file and try again."
There is no other program open at the time.