Wont go to checkout - only to shopping cart

I've recently moved a 3.0.2.0 website to a new host,

since then, intermitently, we get an error where customers cannot go to the checkout page. When it happens, we can only go to the cart. Whenever we try to go to the checkout, we get directed back to the cart.

It appears it can be solved by wiping browser cache, but this isn't really ideal for customers.

Any idea what could be causing this? This didn't happen previously.

Dave

Could be to do with /tmp session files on your new host, are they any good at support?