launchd won't run a loaded script on reboot
Check your permissions. The file script.plist should look like this

-rw-r--r--  1 wheel  410 16 ... 

From man launchctl


  Note that per-user configuration files (LaunchAgents) must be owned by the user loading them. All system-wide daemons (LaunchDaemons) must be owned by root. Configuration files must not be group- or world-writable.