PayPal Pro API version possibly causing 10540 err

-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.8
-- PHP version -- : 5.5.30
-- Error-message(debug-mod must be tuned on) -- : Error 10540: The transaction cannot be processed due to an invalid address

Hello,
We are getting lots of rejected PayPal Pro transactions with "Error 10540: The transaction cannot be processed due to an invalid address." and having contacted PayPal about this they are not sure what the problem is but they say we are running a really old version of the API (51) and we need to try 200. Looking at their changelog, 51 is so old it isn't even on it anymore and it goes back to 2012, so maybe they have a point.
So, how can we change the version to 200?

Hello,
After checking that link : developer.paypal.com/docs/classic/api/NVPAPIOverview/
I think that you should edit the "paypalpro.php" file of the PayPal Pro plugin and change that line :

	'VERSION' => '51.0',

	'VERSION' => '200',

Hello,

We changed the line to '200' and got a different error message:

Error 10006: Version is not supported. See attached screenshot.

We also noted on the PayPal site, we could set the version to '201' or '202' etc. We tried this but it did not work either.

Do you have any further suggestions?

Thanks