it's probably macosx with the dmg error. the admin message means it lacks write permissions. and you lack those in linux main binary folder (or if installed as admin without changing the permissions after), in windows vista and 7 with a default account when installed in program files (with uac enabled, and without using the disabled "Administrator" account), in previous supported windows if not using the main account (without reconfiguration) and on macosx for system wide installs. Actually applications and games always required admin permissions to install and update except if installed in home folders of the user or if the os had the file protections options misconfigured (eg running always as full admin in xp, or root on linux, wrong permissions setup for critical folders...)