[BUG-Add to Cart] Causing javascripts to break when clicked

I tried to use a jquery plugin for the shop but it kept breaking once "Add to Cart" was clicked. I tried deleting all JS & CSS code and just go with a plain html page but same error kept popping up.

On Firefox i dont get any error message, but the same issue occurs.

Any ideas?

This is straight from the chrome console

1. Refused to set unsafe header "Connection" prototype-core.ashx:579
   1. AjaxPro.Request.invokeprototype-core.ashx:579
   2. AjaxPro.AjaxClass.invokeprototype-core.ashx:690
   3. Object.extend.Object.extend.ServerSideAddItemToOrderCMS.CatalogueRetrieve,Catalyst.Web.CMS.ashx:6
   4. AddToCartJava_OnlineShopping.js?vs=b2364.r426701:1
   5. onclickitem-3:1

2.  

   The part chrome is complaining about in prototype-core.ashx:579

   if(!MS.Browser.isIE) {

3.   this.xmlHttp.setRequestHeader("Connection", "close"); // Mozilla Bug #246651

4. }