You may want to try logging into the sandbox area and generating a new set of credentials, the ones that you have might not be valid for Direct Pay testing. If you have any further issues with this let me know and I will get a ticket opened for you so we can do some more specific testing to determine what the problem is.
In the WAGlobal file - Test mode = false, and sandbox = true.
I've deleted the previous credentials and done new ones for the store and customers, and again I can purchase from the express checkout, but not direct pay. The only thing I am left to edit is changing 'states' for 'county's to make it for the UK, but am yet to edit the code, until I can get it right first from how you have it set up originally.
I would really appreciate it if you could open a ticket for me please, as I have been working on this for 6 months for a client after 2 months of trying to open a paypal account went by, yet I am so close to the finish, I can see the light, lol! Let us know what I have to do please.