getElementById variable

Hi,
I've been banging my head against a wall for hours on this and can't work out how it's done so can someone please help me?

I call a javascript function using embedded javascript in HTML as follows:

<SCRIPT LANGUAGE="JAVASCRIPT" TYPE="TEXT/JAVASCRIPT">
<!--
window.onload = function ()
{
initSlideDownMenu("accordionactivity");
}
//-->
</SCRIPT>

Code (markup):

The function is in a separate javascript file. When the first alert pops up I get 'accordionactivity', when the second one pops up I get '[object]' but when the third one pops up I get 'null'. The rest of the function fails to work properly too:

function initSlideDownMenu(slMenuName)
{

alert(slMenuName);
alert(document.getElementById('accordionactivity'));
alert(document.getElementById(slMenuName));

 dhtmlgoodies_slmenuObj = document.getElementById(slMenuName);
 dhtmlgoodies_slmenuObj.style.visibility='visible';
 var mainUl = dhtmlgoodies_slmenuObj.getElementsByTagName('UL')[0];  
 var mainMenuItem = mainUl.getElementsByTagName('LI')[0];
 mainItemCounter = 1;
 while(mainMenuItem){   
  if(mainMenuItem.tagName=='LI'){
   var aTag = mainMenuItem.getElementsByTagName('A')[0];
   var subUl = mainMenuItem.getElementsByTagName('UL');
   if(subUl.length>0){
    mainMenuItem.id = 'mainMenuItem' + mainItemCounter;
    initSubItems(subUl[0],2);
    aTag.onclick = showSubMenu;
    mainItemCounter++;
   }    
  }   
  mainMenuItem = mainMenuItem.nextSibling; 
 }  
 
 if(location.search.indexOf('mainMenuItemToSlide')>=0){
  var items = location.search.split('&');
  for(var no=0;no<items.length;no++){
   if(items[no].indexOf('mainMenuItemToSlide')>=0){
    values = items[no].split('=');
    showSubMenu(false,document.getElementById('mainMenuItem' + values[1])); 
    initMenuIdToExpand = false;    
   }
  }   
 }else if(expandFirstItemAutomatically>0){
  if(document.getElementById('mainMenuItem' + expandFirstItemAutomatically)){
   showSubMenu(false,document.getElementById('mainMenuItem' + expandFirstItemAutomatically));
   initMenuIdToExpand = false;
  }
 }

 if(expandMenuItemByUrl)
 {
  var aTags = dhtmlgoodies_slmenuObj.getElementsByTagName('A');
  for(var no=0;no<aTags.length;no++){
   var hrefToCheckOn = aTags[no].href;
   if(location.href.indexOf(hrefToCheckOn)==0 && (location.href.length==hrefToCheckOn.length || location.href.indexOf('?')==hrefToCheckOn.length)){
    initMenuIdToExpand = false;
    var obj = aTags[no].parentNode;
    while(obj && obj.id!=slMenuName){
     if(obj.tagName=='LI'){       
      var subUl = obj.getElementsByTagName('UL');
      if(initialMenuItemAlwaysExpanded)alwaysExpanedItems[obj.parentNode] = true;
      if(subUl.length>0){        
       objectsToExpand.unshift(obj);
      }
     }
     obj = obj.parentNode; 
    }
    showSubMenu(false,objectsToExpand[0]);
    break;     
   }   
  }
 }
   
 if(initMenuIdToExpand)
 {
  objectsToExpand = new Array();
  var obj = document.getElementById(initMenuIdToExpand)
  while(obj && obj.id!=slMenuName){
   if(obj.tagName=='LI'){
    var subUl = obj.getElementsByTagName('UL');
    if(initialMenuItemAlwaysExpanded)alwaysExpanedItems[obj.parentNode] = true;
    if(subUl.length>0){      
     objectsToExpand.unshift(obj);
    }
   }
   obj = obj.parentNode; 
  }
  showSubMenu(false,objectsToExpand[0]);
 }
}

Code (markup):

I've tried using slMenuName.toString() and appending quotes before and after the variable but nothing works.
Can you help me get this working?

Thank you

 

Can you write here html code too?