unlink permission problems

I have a function that compares two files, and deletes the first if they are identical. The problem is, that whenever the function attempts to unlink the file it causes an error "unlink(<filename>): Permission denied". I first tried this using an Administrator account. Then to be sure I tried a user account, creating the files in that account before running the script. I can see no reason why permission is denied. Anyone have an idea? Niel Archer