In case a file that you're trying to change ownership on, belongs to the other user, you can not change it to yourself, unless you run the command as administrator
(that user) or root
user!
Besides your username contains spaces - that's not allowed on NIX systems. Username should follow the rule:
([a-z_][a-z0-9_]{0,30})
Moreover the username must exist. Try checking if user that you're refering to is really registered:
cat /etc/passwd |grep username