Yeah, some seem broken, but intermittently.
Couple of observations… Why oh why a frame? This will never ever do you any favours! Why not use Magento’s multi-shop functionality?
I wouldn’t be surprised if the cross usage of domains like ppserver and premium-portfolio is causing you this grief.
The last tags rendered on broken pages consistently is this:
<form action="http://www.ppserver.co.uk/system/index.php/rslr0011/checkout/cart/add/uenc/aHR0cDovL3d3dy5wcHNlcnZlci5jby51ay9zeXN0ZW0vaW5kZXgucGhwL3JzbHIwMDExL3dyaXRpbmctaW5zdHJ1bWVudHMvcGxhc3RpYy1wZW5zL3BuMDAzNC1kb2hhLXBsYXN0aWMtcGVuLXdpdGgtbGFyZ2UtY2xpcC5odG1sP19fX1NJRD1V/product/1075/?___SID=U" method="post" id="product_addtocart_form">
<p class="product-image product-image-zoom">
Seems to me something is wrong with your zoomer. At least it narrows it down nicely.
Also note typo in your title tags, portfoilo.