IE error, bugs

So i'm having heavy problems with accesing page on Internet explorer, IE is reporting several error like this:

<script type="text/javascript">
$(document).ready(function(){

if($('.subDropdown')[0]){
$('.subDropdown').click(function(){
$(this).toggleClass('plus');
$(this).toggleClass('minus');
$(this).parent().find('ul').slideToggle();
});
}

});

It's reporting that $ function isn't set yet... And i'm not a pro for web building so I don't know how to fix it.

Page on Lamby theme is having problems when on IE and trying to open product page and category page...
Its disturbing because still a lot of companies uses IE....

I would be really happy If I could solve this problem, so good people of the internet, share your wisdom with me

Since this is a paid Custom Theme, I guess, you better contact :
http://themeforest.net
because only experienced Proples, knowing/using the same Theme,
would possibly have an idea..., since it's not OC DEFAULT code, you show above, either!
Ernie

Sory, didn't know this forum only for default theme.
Anyway, now i had to pay some guys to try to fix my problem, because authors of the theme aren't responding...

Regards,