No payer information returned from PayPal

Our website is set up not long time again and we are using PayPal Express as the only payment method.

We noticed that one customer failed to pay today and it seems the information returned from PayPal is incorrect. On the email with subjext ec_step2_finish - 1, all the fields returned are empty, below is the array returned,

START: paypal_ec_payer_info= Array
(
[payer_id] =>
[payer_email] =>
[payer_salutation] =>
[payer_gender] =>
[payer_firstname] =>
[payer_lastname] =>
[payer_business] =>
[payer_status] => unverified
[ship_country_code] =>
[ship_address_status] => None
[ship_phone] =>
)

Any help or information leading to a right direction is greatly appreciated.

Have you applied the recent PayPal patches?

Thanks for your prompt feedback Kim,

To answer your question, actually I am using the Zen cart v1.3.7.1 since we just put up the website. I think I do not need to apply the patch c'oz it's up to date.

On another note, we've receive other orders paid for through PayPal Express without problem. It may be a very intermittent problem caused by PayPal, I guess.