So, basically the file you are trying to delete does not exist. Why do you think that is? (Hint: what do you see when you print $file within the loop?)

Your problem is that readdir returns the names of the files; not their full paths, so what your code is trying to do is delete a filename read from a path on your V: drive, from your current directory.

You need to combine the name returned from readdir, with the path you gave to opendir to get a full pathname.

Something like this might work:

...
     foreach $file (readdir DH){
        my $path = "$dir_to_process/$file";
        unlink $path or warn "failed on $path: $!\n"
            if -M $path > 14;
        
    }
[download]

And for future reference, investigate glob which makes doing this sort of thing much easier.