VSFTPD says "500 OOPS: cannot change directory"
Solution 1:
Looks like in order for the user to be able to be chroot'd to the directory configured, all the parent directories must have read and execute permissions, otherwise they will be denied for security reasons.
Solution 2:
I think your users are going to be bound to their home directories with chroot_local_user=YES, maybe try setting your ftp user's home directory to /data/some-path/ftp/data/$USER else see what happens when with chroot_local_user=NO