Try to add an envent listener for 'load' instead, or use the declarative syntax <body onload="init()">.
EDIT: Additionally, saying window.onload = init(); sets window.onload to the result of calling init(). What you mean is window.onload = init; (a lambda expression). This is bad practice still, as it overwrites other things that might be bound to window.onload.
I'm no javascript master, but I usually setup onload functions like so:
window.onload = function() { init(); }
Doing it your way appears to execute the function, then set the return value to the window.onload property.
Shouldn't line 82 read:
window.onload = init;
When you do "init()" it's a call to a function that returns void. You end up calling that function before the page loads.
In addition to the onload fixes proposed here, also check to see if there are multiple elements with that ID, I believe IE will return a collection of all elements with that ID, in which case you would need to select the intended item out of the collection before accessing that property or ensure you are using unique IDs.
To preserve any previously set onload functions try this
var prevload = window.onload;
window.onload = function(){
prevload();
init();
}