Checkout keeps failing

Hi,

I am trying to finalise a transaction with express checkout. I have everything set up correctly I think. I am using sandbox and I can initiate the transaction, I then log into my testing buyer account and proceed, it takes me back to the confirm page which is all filled out correctly from the token. It is when I press the Submit Order button on the pp_confirm.php page it ends up redirecting me to the pp_checkout_failure.php page.

Has anybody experienced this before and have any idea what it might be. Is there some way I can find out what error is occuring is there a log or something I can look through? I just end up on that page with no error messages or indications why. Could it perhaps be a setting I need to change in my sandbox accounts?

I am using ecart 4 and I am in Australia incase that makes a difference.