Netscape - innerHTML

Hi,

I've a problem with a JS function that works well with IE but not with
Netscape 7.
Here is the code :
function ChangeMessage(){
if (document.getElementById){
document.getElementById("box1").innerHTML = "message";
}
}

With this code, under Netscape, it displays twice "message" in my DIV !!!
And if I call again this function, it displays nothing.

I really can't undertsand why....I someone have an idea...

Thanks.