Zen Cart 1.3.7.1 Shipping Address Country Empty

I am still very new to Zen Cart, please bear with me. I am getting the "Shipping Address Country Empty" error even though I am on the latest version of zencart - version 1.3.7.1. I have set up paypal express and I am testing the payment module using sandbox

Here is the debug file:
function: before_process() - Express Checkout

Value List:
array (
'ITEMAMT' => '25.00',
'SHIPPINGAMT' => '2.50',
'AMT' => '27.50',
'L_NUMBER0' => '0',
'L_QTY0' => '1',
'L_NAME0' => 'Who's got my bone? bath towel
Message 1: test
Text Colour: Red
Font Style: Kids Only',
'L_AMT0' => '25.00',
'L_TAXAMT0' => '0.00',
'SHIPTONAME' => 'Mary John',
'SHIPTOSTREET' => '320 Cricklewood Lane',
'SHIPTOSTREET2' => 'London',
'SHIPTOCITY' => 'london',
'SHIPTOSTATE' => '',
'SHIPTOZIP' => 'NW2 2QE',
'SHIPTOCOUNTRY' => '',
'BUTTONSOURCE' => 'ZenCart-EC_us',
'TOKEN' => 'EC-4CT827013P008064K',
'PAYERID' => 'YWDGQHWELHKJY',
'PAYMENTACTION' => 'Sale',
'NOTIFYURL' =>
'http://www.candycherub.com/candyshop/ipn_main_handler.php',
'METHOD' => 'DoExpressCheckoutPayment',
'CURRENCYCODE' => 'GBP',
'USER' => 'sell_1195050329_biz_api1.candycherub.com',
'PWD' => '****************',
'VERSION' => '2.3',
'SIGNATURE' => '****************************************************2R2r',
)

Response:
Array
(
[TIMESTAMP] => 2007-11-18T22:10:38Z
[CORRELATIONID] => eb29b188781a1
[ACK] => Failure
[L_ERRORCODE0] => 10731
[L_SHORTMESSAGE0] => Shipping Address Country Empty
[L_LONGMESSAGE0] => The field Shipping Address Country is required
[L_SEVERITYCODE0] => Error
[VERSION] => 2.300000
[BUILD] => 1.0006
)

Thanks for any help!

What country was selected by the customer?
What changes have you made with respect to countries in your Zen Cart admin?
What addons/contributions have you installed?
In what ways have you customized your cart?

DrByte,
Thanks for responding.

In response to your questions:

What country was selected by the customer?
The test account has UK as the country. I set up UK as the default country in Create Account Default Country ID.

What changes have you made with respect to countries in your Zen Cart admin?
I set UK as the Country of Origin a
What addons/contributions have you installed?
I haven't installed any addons or contributions
In what ways have you customized your cart?
The modifications I have done have been mainly confined to the stylesheet.

Thanks

"UK" is not a valid country code according to PayPal. "GB" (or "GBR" for 3-letter code) is.
PayPal probably sent "GBR" back as the country code, but perhaps your store doesn't recognize that because you've changed or pared-down country entries?

Dr Byte,

In saying UK , I selected United Kingdom as the default country. I noticed the that the debug file has [LOCALECODE] => US, could this be a problem?

Sorry if I sound ignorant, what do you mean by a parred down version?

What do you have in your Admin under Localization/Taxes->Countries ... for "United Kingdom"? What are the 2-letter and 3-letter codes?
And, have you added or removed any countries from this list?

The 2 letter code is GB, the 3 letter code is GBR. I haven't removed any countries from the list. There are about 12 pages of countires.

Thanks

DrByte:

What country was selected by the customer?
What changes have you made with respect to countries in your Zen Cart admin?
What addons/contributions have you installed?
In what ways have you customized your cart?

Same problem as me, this is a different thread to one I posted to earlier.
http://www.zen-cart.com/forum/showpost.php?p=670714&postcount=41

In answer to this one of the two failed orders,
One customer chose United Kingdom (the default set)
The other one looks blank
No changes to countries in zen-cart (cannot understand zones)
image handler & edited templates for visual text only.
Same error code as this user in this thread.

If you are having problems with this one go to this thread where its shows how to solve the issue.

http://www.zen-cart.com/forum/showthread.php?p=504386#post504386