I have the same problem, but I've tried everything suggested in the above solution and I still have the same problem, nothing is getting transferred to PayPal properly. My default currency is CA (Canadian) and I have in catalog/includes/languages/english.php set to:
// if USE_DEFAULT_LANGUAGE_CURRENCY is true, use the following currency, instead of the applications default currency (used when changing language)
define('LANGUAGE_CURRENCY', 'CA');
and in Admin - My Store I have
Switch To Default Language Currency = true
What else am I missing? Please help!!