DHL is not working with production API url

Question

I'm stuck on this issue with DHL on Magento 1.7.1 :

Symptoms:

• If I use the test DHL API url I got the a correct response from DHL (https://xmlpitest-ea.dhl.com/XMLShippingServlet)
• if I use the production DHL API url (https://xmlpi-ea.dhl.com/XMLShippingServlet) the XML request is correctly created by Magento but I got no XML response from DHL.

Details:

• DHL response is empty
• an exception is trigger by and cached in Zend_Http_Response(579) and then caught in Mage_Usa_Model_Shipping_Carrier_Dhl_International(849):
  Error parsing body - doesn't seem to be a chunked message

I contacted DHL but they say everything is correct on their side.

Any one is experiencing same problem ? what I should check ?

Thanks you in advance