Assume that your form action url is checkout/cart/updatePost/ and have no customization at Mage_Checkout_CartController at updatePostAction().

Then you need to understand that magento checkout/cart/updatePost does not render Cart page content.so if you have try to get cart page content from checkout/cart/updatePost/ then it become waste of time.

Because of checkout/cart/updatePost is response 302 after done anything.So your case you need to customization at cart controller

Also,as you have use magento 1.9 then you need to check form_key field is available or not in that form

Assume that your form action url is checkout/cart/updatePost/ and have no customization at Mage_Checkout_CartController at updatePostAction().

Then you need to understand that the request to checkout/cart/updatePost does not render the cart page content. So if you tried to get the cart page content from the response, it's a waste of time. The response is a 302 redirect after the cart was updated.

So you need to use a customized cart controller.

Also make sure, that the form_key input field is present.

Assume that your form action url is checkout/cart/updatePost/ and have no customization at Mage_Checkout_CartController at updatePostAction().

Then you need to understand that magento checkout/cart/updatePost does not render Cart page content.so if you have try to get cart page content from checkout/cart/updatePost/ then it become waste of time.

Because of checkout/cart/updatePost id response 302 after done anything.So you case you need to customization at cart controller

Also,as you have use magento 1.9 then you need to check form_key is available or not at form

Assume that your form action url is checkout/cart/updatePost/ and have no customization at Mage_Checkout_CartController at updatePostAction().

Then you need to understand that magento checkout/cart/updatePost does not render Cart page content.so if you have try to get cart page content from checkout/cart/updatePost/ then it become waste of time.

Because of checkout/cart/updatePost is response 302 after done anything.So your case you need to customization at cart controller

Also,as you have use magento 1.9 then you need to check form_key field is available or not in that form