Cannot connect to paypal sandbox

My paypal sandbox was working fine. Now following the shipping information page I get a blank page with the "checkout now" button (strange) and after clicking on it (again) I am receiving the following error:
"There was a problem connecting to PayPal to setup your purchase. Please try again."
There are no other error codes/messages. I have recently updated the MarketPress plugin from v2.8.8 to v2.9.2.5 to v2.9.2.6. I am running this on a multisite using WordPress v 3.8.1. The link to the store is here: