rc.local doesnt run at boot start up

[mikecarlone]

if i run the command " update-rc.d rc.local defaults "

then i get

" update-rc.d: warning: rc.local stop runlevel arguments (0 1 6) do not match LSB Default-Stop values (none)
System start/stop links for /etc/init.d/rc.local already exist.

"

how can i start rc.local at boot up