Provided shipping address error

We are having problems on our checkout page when a customer goes to place order and the page throws an error:

Please fix the following error before continuing

• There was a problem with the provided shipping address: is required

We have tried disabling some fields required for shipping and also purging cache to see if it is a caching issue but the error has refused to go away.

Please assist us diagnose what the error could be about.

The page I need help with: [log in to see the link]