Mobile Site Hangup

My reponsive site works ok till I try to go from the cart pg to checkout on my I phone. I have no problem with my kindle tablet.

can you tell me what to look at to solve this problem?

Thank you

What kind of problem do you have? And what theme do you use?

I am using the responsive theme with modern settings. When I try to go from the cart to checkout the iphone starts to go but it locks before I reach the checkout page. The url is primequalityproducts.com/403

Thank you

e-com I didn't mention that the responsive/modern has been upgraded to 4.8.1