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When I add a item in the cart it shows up on the cart, when I clink on the cart button instead of Checkout, the page goes blank. If I click on the checkout, it takes me Login Page on the checkout process. If I click on the Summary page the page goes blank again.

The problem is solved if I login as customer.

Please help as it is really important, as many of my customers want to use the vouchers but they can’t becasue of the issue. therefore i am loosing lots of sales