Paypal Express not going anywhere

Hi Guys:
When I checkout by Paypal express, I have got the following error message in error log.
Paypal express is just not processing at all. It just reload checkout page.
Anyone can help please?

2014-12-04 15:45:55 - PayPal Express debug (Call data): {"METHOD":"SetExpressCheckout","MAXAMT":"0.00","RETURNURL":"http:\/\/www.svensisland.com\/index.php?route=payment\/pp_express\/checkoutReturn","CANCELURL":"http:\/\/www.svensisland.com\/index.php?route=checkout\/checkout","REQCONFIRMSHIPPING":0,"NOSHIPPING":1,"LOCALECODE":"EN","LANDINGPAGE":"Login","HDRIMG":null,"HDRBORDERCOLOR":"","HDRBACKCOLOR":"","PAYFLOWCOLOR":"","CHANNELTYPE":"Merchant","ALLOWNOTE":"1","PAYMENTREQUEST_0_SHIPPINGAMT":"","PAYMENTREQUEST_0_CURRENCYCODE":"AUD","PAYMENTREQUEST_0_PAYMENTACTION":"Sale","L_PAYMENTREQUEST_0_DESC0":"","L_PAYMENTREQUEST_0_NAME0":"Lip Balmy- (Tube)","L_PAYMENTREQUEST_0_NUMBER0":"LP5","L_PAYMENTREQUEST_0_AMT0":"6.95","L_PAYMENTREQUEST_0_QTY0":1,"L_PAYMENTREQUEST_0_ITEMURL0":"http:\/\/www.svensisland.com\/the-goods\/lip-balmy-tube","L_PAYMENTREQUEST_0_ITEMWEIGHTVALUE0":"0.00","L_PAYMENTREQUEST_0_ITEMWEIGHTUNIT0":"kg","L_PAYMENTREQUEST_0_DESC1":"","L_PAYMENTREQUEST_0_NAME1":"Lip Balmy- (Tin) ","L_PAYMENTREQUEST_0_NUMBER1":"LP12","L_PAYMENTREQUEST_0_AMT1":"9.95","L_PAYMENTREQUEST_0_QTY1":1,"L_PAYMENTREQUEST_0_ITEMURL1":"http:\/\/www.svensisland.com\/the-goods\/lip-balmy-tin","L_PAYMENTREQUEST_0_ITEMWEIGHTVALUE1":"0.00","L_PAYMENTREQUEST_0_ITEMWEIGHTUNIT1":"kg","L_PAYMENTREQUEST_0_NUMBER2":"shipping","L_PAYMENTREQUEST_0_NAME2":"Parcel Post Small (500g) Satchel","L_PAYMENTREQUEST_0_AMT2":"8.25","L_PAYMENTREQUEST_0_QTY2":1,"PAYMENTREQUEST_0_ITEMAMT":"25.15","PAYMENTREQUEST_0_AMT":"25.15"}
2014-12-04 15:45:56 - PayPal Express debug (Result): "TIMESTAMP=2014%2d12%2d04T04%3a45%3a57Z&CORRELATIONID=3e407a3b92b7c&ACK=Failure&VERSION=65%2e2&BUILD=14086142&L_ERRORCODE0=10002&L_SHORTMESSAGE0=Security%20error&L_LONGMESSAGE0=Security%20header%20is%20not%20valid&L_SEVERITYCODE0=Error"

Solved. Compared the error code with paypal code page. turns out the api was not correct.