Magento Soap API works locally but not remotely

I created my own API for Magento Enterprise 1.11. The API call via Soap v1 works fine on local, but I cannot make calls from local to remote.

Using PHP interactive shell on my localdev:

php > $client = new SoapClient(WSDL_URI,array('trace'=>1));
php > $client->login(API_USER,API_KEY);
php > var_dump($client->__getLastResponse());
string(538) "<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="urn:Magento" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><SOAP-ENV:Body><ns1:loginResponse><loginReturn xsi:type="xsd:string">f0eec73e49665aaf9cc4a6644fba5dc6</loginReturn></ns1:loginResponse></SOAP-ENV:Body></SOAP-ENV:Envelope>

      

        
        
        
      

    

I was able to do this successfully from localhost as well as between two local VMs running on my dev machine. I can also access my custom API methods without issue.

However, when I try to make a soap client for my remote test environment, I can create the client, but calling the $ client-> login () method, or any subsequent call, results in the following:

php > $client = new SoapClient(REMOTE_WSDL_URI,array('trace'=>1));
php > $client->login(API_USER,API_KEY);
PHP Warning:  Uncaught SoapFault exception: [WSDL] SOAP-ERROR: Parsing WSDL: Couldn't load from 'http://REMOTE_HOST/index.php/api/index/index/wsdl/1/' : failed to load external entity "http://REMOTE_HOST/index.php/api/index/index/wsdl/1/" in php shell code:1
Stack trace:
#0 php shell code(1): SoapClient->__call('login', Array)
#1 php shell code(1): SoapClient->login(API_USER, API_KEY)
#2 {main}
php > var_dump($client->__getLastRequestHeaders());
string(255) "POST /index.php/api/index/index/ HTTP/1.1
Host: REMOTE_HOST
Connection: Keep-Alive
User-Agent: PHP-SOAP/5.3.18-1~dotdeb.0
Content-Type: text/xml; charset=utf-8
SOAPAction: "urn:Mage_Api_Model_Server_HandlerAction"
Content-Length: 550

php > var_dump($client->__getLastResponseHeaders());
string(840) "HTTP/1.1 500 Internal Service Error
Date: Mon, 11 Feb 2013 19:06:56 GMT
Server: Apache/2.2.16 (Debian)
X-Powered-By: PHP/5.3.19-1~dotdeb.0
Set-Cookie: PHPSESSID=7uqrcmiv96hroubnb1uu7c7cm6; expires=Wed, 13-Feb-2013 01:06:56 GMT; path=/; domain=.REMOTE_HOST; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: CUSTOMER=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; path=/; domain=.REMOTE_HOST; httponly
Set-Cookie: CUSTOMER_INFO=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; path=/; domain=.REMOTE_HOST; httponly
Set-Cookie: CUSTOMER_AUTH=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; path=/; domain=.REMOTE_HOST; httponly
Content-Length: 468
Vary: Accept-Encoding
Connection: close
Content-Type: text/xml; charset=utf-8

php > var_dump($client->__getLastResponse());
string(468) "<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"><SOAP-ENV:Body><SOAP-ENV:Fault><faultcode>WSDL</faultcode><faultstring>SOAP-ERROR: Parsing WSDL: Couldn't load from 'http://REMOTE_HOST/index.php/api/index/index/wsdl/1/' : failed to load external entity "http://REMOTE_HOST/index.php/api/index/index/wsdl/1/"
</faultstring></SOAP-ENV:Fault></SOAP-ENV:Body></SOAP-ENV:Envelope>

      

        
        
        
      

    

When I find // REMOTE _HOST / index.php / api /? Wsdl I get the standard Magento WSDL.

Both environments have the same 99.99%:

• Server version: Apache / 2.2.16 (Debian) (both local and remote)
• PHP 5.3.18 (local dev) 5.3.19 (remote host)
• Apache / PHP configurations are the same.
• The code base is identical

I have counted intewebs for clues, including:

• http://www.magentocommerce.com/boards/viewthread/56528/
• http://www.magentocommerce.com/wiki/5_-_modules_and_development/web_services/overriding_an_existing_api_class_with_additional_functionality#wsdl
• Failed to connect to Magento SOAP API v2 due to "could not load external object"
• Magento API SOAP-ERROR: WSDL Parsing: Failed to load from [url] /index.php/api/index/index/?wsdl=1 ': Couldn' t find end of tag line start tag 56
• http://www.magentocommerce.com/api/soap/introduction.html

I've tried the Content-Length header fix mentioned in the sedond-to-last link and pretty much anything I could think of ... Stumped.