errore getElementById

[d4ve]

Ciao a tutti.

Ho inserito questo menù nel mio sito.

Con IE funziona... però mi segnala un errore nel js che dice:

'document.getElementById(...)' è nullo o non è un oggetto.



Il codice è:

<script type="text/javascript">


var persistmenu="yes" //"yes" or "no". Make sure each SPAN content contains an incrementing ID starting at 1 (id="sub1", id="sub2", etc)
var persisttype="local" //enter "sitewide" for menu to persist across site, "local" for this page only

if (document.getElementById){
document.write('<style type="text/css">\n')
document.write('.submenu{display: none;}\n')
document.write('</style>\n')
}

function SwitchMenu(obj){
    if(document.getElementById){
    var el = document.getElementById(obj);
    var ar = document.getElementById("masterdiv").getElementsByTagName("span"); 
        if(el.style.display != "block"){ 
            for (var i=0; i<ar.length; i++){
                if (ar[i].className=="submenu") 
                ar[i].style.display = "none";
            }
            el.style.display = "block";
        }else{
            el.style.display = "none";
        }
    }
}

function get_cookie(Name) { 
var search = Name + "="
var returnvalue = "";
if (document.cookie.length > 0) {
offset = document.cookie.indexOf(search)
if (offset != -1) { 
offset += search.length
end = document.cookie.indexOf(";", offset);
if (end == -1) end = document.cookie.length;
returnvalue=unescape(document.cookie.substring(offset, end))
}
}
return returnvalue;
}

function onloadfunction(){
if (persistmenu=="yes"){
var cookiename=(persisttype=="sitewide")? "switchmenu" : window.location.pathname
var cookievalue=get_cookie(cookiename)
if (cookievalue!="")
document.getElementById(cookievalue).style.display="block"
}
}

function savemenustate(){
var inc=1, blockid=""
while (document.getElementById("sub"+inc)){
if (document.getElementById("sub"+inc).style.display=="block"){
blockid="sub"+inc
break
}
inc++
}
var cookiename=(persisttype=="sitewide")? "switchmenu" : window.location.pathname
var cookievalue=(persisttype=="sitewide")? blockid+";path=/" : blockid
document.cookie=cookiename+"="+cookievalue
}

if (window.addEventListener)
window.addEventListener("load", onloadfunction, false)
else if (window.attachEvent)
window.attachEvent("onload", onloadfunction)
else if (document.getElementById)
window.onload=onloadfunction

if (persistmenu=="yes" && document.getElementById)
window.onunload=savemenustate

</script> 

Cos'è che fa scattar quel messaggio di errore?