Page Layouts control the location of all elements in the Shopping Cart. All extra code added needs to be surrounded in <literal> </literal> Tags. Code is parsed with xml and certain elements cannot be parsed.
Elements that cannot be parsed - , &, border=0.
If you are unable to access the Shopping Cart, remove the code and check for invalid characters.
Example: To add in the Email Subscribe widget, open Page Layouts and add the widget's code to the left or right sidebar. To define sidebars, add below closing tag of </search> or </shoppingcart>
<emailOptinSmall Title="Signup for our free Newsletter" SubmitButtonText="Newsletter Signup"> </emailOptinSmall>
Remember: Any unclosed selectors will not allow the xml to parse and it will break the shopping cart. Before adding code, make sure all selectors are closed.