If you do not use VPASP's in built horizontal menu, you may receive a javascript error such as:
'document.getElementById(...)' is null or not an object
If the VPASP horizontal menu system is not being used, you should remove the reference to dropdown.js in your shoppage_header.htm file.
You may also experience a similar issue if you do use the VPASP horizontal navigation system, but have altered the logo used on your site.
You should ensure that the logo image tag also includes an id reference of id="logo"