chown: changing ownership not permitted, even though running as root
Solution 1:
I don't think VFAT supports the type of permissions you're trying to set. In such case, the permissions are set the same for all files, when mounting the disk. Something like:
sudo mount -t vfat -o uid=piftp,gid=piftp /dev/sda1 /var/www
See also Can't change permission/ownership/group of external hard drive on Ubuntu here on Super User, or the external resource Connect your Raspberry Pi to a USB hard disk.
Solution 2:
OP wrote:
I solved my ftp problem by mounting with
umask 0000