404 Error in Preview Site & PayPal Sandbox

I am sure I am making another silly mistake, but cannot figure it out.

I am testing with my preview website at http://www.bayareatamilmanram.org.previewdns.com and PayPal Sandbox. When I pay with credit card everything works fine and control returns to my site.

When I pay with PayPal I am getting 404 error: http://www.bayareatamilmanram.org/sample-page/?s2member_paypal_xco=s2member_pro_paypal_checkout_return&token=EC-3XE30370CL576414F&PayerID=RV97HFPV62GNL

I suspect it is to do with the fact that the return URL is not the preview site URL. Not sure how to fix it. Please help.

The only log I see is the PayPal API log. Here it is:
PHP v5.3.14 :: WordPress® v3.5 :: s2Member® v121213 :: s2Member® Pro v121213
Memory 3.18 MB :: Real Memory 3.50 MB :: Peak Memory 3.21 MB :: Real Peak Memory 3.50 MB
http://www.bayareatamilmanram.org/sample-page/
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
——– Input vars: ( Wed Jan 2, 2013 8:30:31 am UTC ) ——–
array (
‘METHOD’ => ‘SetExpressCheckout’,
‘RETURNURL’ => ‘http://www.bayareatamilmanram.org/sample-page/?s2member_paypal_xco=s2member_pro_paypal_checkout_return’,
‘CANCELURL’ => ‘http://www.bayareatamilmanram.org/sample-page/?s2member_paypal_xco=s2member_pro_paypal_checkout_cancel’,
‘PAGESTYLE’ => ‘paypal’,
‘LOCALECODE’ => ”,
‘NOSHIPPING’ => ‘1’,
‘SOLUTIONTYPE’ => ‘Sole’,
‘LANDINGPAGE’ => ‘Billing’,
‘ALLOWNOTE’ => ‘0’,
‘PAYMENTREQUEST_0_PAYMENTACTION’ => ‘Sale’,
‘PAYMENTREQUEST_0_DESC’ => ‘Annual Membership – $50 USD / per family per year’,
‘PAYMENTREQUEST_0_CUSTOM’ => ‘www.bayareatamilmanram.org’,
‘PAYMENTREQUEST_0_CURRENCYCODE’ => ‘USD’,
‘PAYMENTREQUEST_0_ITEMAMT’ => ‘50.00’,
‘PAYMENTREQUEST_0_TAXAMT’ => ‘0.00’,
‘PAYMENTREQUEST_0_AMT’ => ‘50.00’,
‘L_PAYMENTREQUEST_0_QTY0’ => ‘1’,
‘L_PAYMENTREQUEST_0_NAME0’ => ‘Annual Membership – $50 USD / per family per year’,
‘L_PAYMENTREQUEST_0_NUMBER0’ => ‘1::1 Y’,
‘L_PAYMENTREQUEST_0_AMT0’ => ‘50.00’,
‘PAYMENTREQUEST_0_SHIPTONAME’ => ‘SivaThree TestThree’,
‘PAYMENTREQUEST_0_SHIPTOSTREET’ => ”,
‘PAYMENTREQUEST_0_SHIPTOCITY’ => ”,
‘PAYMENTREQUEST_0_SHIPTOSTATE’ => ”,
‘PAYMENTREQUEST_0_SHIPTOCOUNTRYCODE’ => ‘US’,
‘PAYMENTREQUEST_0_SHIPTOZIP’ => ”,
‘EMAIL’ => ‘seshappan@hotmail.com’,
‘VERSION’ => ‘71.0’,
‘USER’ => ‘pro_1356973562_biz_api1.gmail.com’,
‘PWD’ => ‘1356973619’,
‘SIGNATURE’ => ‘ARL5rz4IL098uQpoQEp53ELB8K6oAPsnmSD..eSkyD6t8W.Nx5wmnzrP’,
)
——– Output string/vars: ( Wed Jan 2, 2013 8:30:32 am UTC ) ——–
TOKEN=EC%2d3XE30370CL576414F&TIMESTAMP=2013%2d01%2d02T08%3a30%3a32Z&CORRELATIONID=2b00a85d948e&ACK=Success&VERSION=71%2e0&BUILD=4181146
array (
‘TOKEN’ => ‘EC-3XE30370CL576414F’,
‘TIMESTAMP’ => ‘2013-01-02T08:30:32Z’,
‘CORRELATIONID’ => ‘2b00a85d948e’,
‘ACK’ => ‘Success’,
‘VERSION’ => ‘71.0’,
‘BUILD’ => ‘4181146’,
)