Being non-root user, you can chgrp a file to any group you belong to, but you can't chown a file.
from the man page:
Only the root user can change the owner of a file. You can change the group of a file only if you are a root
user or if you own the file. If you own the file but are not a root user, you can change the group only to a
group of which you are a member.
I suggest sudo.
HTH,
p5wizard