PayPal Express Checkout integration

I'm having trouble integrating PayPal's Express Checkout. I found the following forum post, which may account for the problem, but no solutions is provided:

Something funky between Dreamhost and Paypal IPN? http://discussion.dreamhost.com/showthreaded.pl?Cat=0&Board=forum_troubleshooting&Number=102433&page=&view=&sb=&o=&vc=1#Post102433

I believe the problem is in the below function, provided by Paypal. Instead of retrieving the needed array, I get redirected to PayPal login.

The other discussion post indicates the problem is with the version of Apache (2.), and suggests that the solution is to move to a server with another version (1.).

Any help or suggestions would be greatly appreciated.

/**
'-------------------------------------------------------------------------------------------------------------------------------------------
* hash_call: Function to perform the API call to PayPal using API signature
* @methodName is name of API method.
* @nvpStr is nvp string.
* returns an associtive array containing the response from the server.
'-------------------------------------------------------------------------------------------------------------------------------------------
*/
function hash_call($methodName,$nvpStr)
{
//declaring of global variables
global $API_Endpoint, $version, $API_UserName, $API_Password, $API_Signature;
global $USE_PROXY, $PROXY_HOST, $PROXY_PORT;
global $gv_ApiErrorURL;

//setting the curl parameters.
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$API_Endpoint);
curl_setopt($ch, CURLOPT_VERBOSE, 1);

//turning off the server and peer verification(TrustManager Concept).
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);

curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_POST, 1);

//if USE_PROXY constant set to TRUE in Constants.php, then only proxy will be enabled.
//Set proxy name to PROXY_HOST and port number to PROXY_PORT in constants.php
if($USE_PROXY)
curl_setopt ($ch, CURLOPT_PROXY, $PROXY_HOST. ":" . $PROXY_PORT);

//NVPRequest for submitting to server
$nvpreq="METHOD=" . urlencode($methodName) . "&VERSION=" . urlencode($version) . "&PWD=" . urlencode($API_Password) . "&USER=" . urlencode($API_UserName) . "&SIGNATURE=" . urlencode($API_Signature) . $nvpStr;

//setting the nvpreq as POST FIELD to curl
curl_setopt($ch, CURLOPT_POSTFIELDS, $nvpreq);

//getting response from server
$response = curl_exec($ch);

//convrting NVPResponse to an Associative Array
$nvpResArray=deformatNVP($response);
$nvpReqArray=deformatNVP($nvpreq);
$_SESSION['nvpReqArray']=$nvpReqArray;

if (curl_errno($ch))
{
// moving to display page to display curl errors
$_SESSION['curl_error_no']=curl_errno($ch) ;
$_SESSION['curl_error_msg']=curl_error($ch);

//Execute the Error handling module to display errors.
}
else
{
//closing the curl
curl_close($ch);
}

return $nvpResArray;
}