Aloha, I don't understand why this simple script occurs error and won't work, can someone help please?

default
{
state_entry()
{
llSensorRepeat("", NULL_KEY, AGENT, "5", PI, 5);
}
sensor(integer total_number)
{
llSay(0,"If you see a black box, enable Advanced Lighting Model in preferences. Turn on sounds to max too. ");

}
}