problem med window.onload event..

jeg får en fejl i det her script:
oldOnload = window.onload;
window.onload = function() {
  if(typeof oldOnload == 'function') oldOnload();
  var ids = arrRoomID.length;
  for(x=0;x<ids;x++) {
    el = document.getElementById('img_RoomID_'+arrRoomID[x]);
    alert(typeof el+'\n'+el.id);
    aE(el,'click','selectCheckBox', 'false');
  }
}

Den linje der fejler er: aE(el,'click','selectCheckBox', 'false');

Fejlen er: uncaught exception: [Exception... "Could not convert JavaScript argument"  nsresult: "0x80570009 (NS_ERROR_XPC_BAD_CONVERT_JS)"  location: "JS frame :: https://www.evaluer.dk/mjCourse_New.asp :: aE :: line 5653"  data: no]

Line 0