The issue is still there and we are  very sure it's on Salesforce's side. We can successfully log onto Salesforce. However we cannot execute any additional requests. Any Queries, but also a request for the server timestamp fail.

Here is our code. We implemented a barebone example using the latest (20) toolkit for PHP, but the same error occurs in our original code with the unchanged older PHP toolkit code.

require_once("sfphp/soapclient/SforceEnterpriseClient.php");
require_once("sfphp/soapclient/SforceHeaderOptions.php");

$oSalesforce = new SforceEnterpriseClient();

print "<p>Created</p>";

if (!$oSalesforce->createConnection("sfphp/soapclient/enterprise.wsdl.xml"))
{
	print "<p>Unable to create a connection</p>";
}

print "<p>Connected</p>";

if (!$oSalesforce->login("name","password"))
{
	print "<p>Unable to log on</p>";
	exit;
}
	
print "<p>Logged On</p>";

print "<p>End Point is " . $oSalesforce->getLocation() . "</p>";

print "<p>Last response is <br/><i> " . $oSalesforce->getLastResponse() . "</i></p>";

print "<p>Server timestamp is <br/><i> " . $oSalesforce->getServerTimestamp() . "</i></p>";

The output is:

Created

Connected

Logged On

End Point is https://eu0-api.salesforce.com/services/Soap/c/20.0/00D200000000MSH

Last response is 
https://eu0-api.salesforce.com/services/Soap/m/20.0/00D200000000MSHfalsefalsehttps://eu0-api.salesforce.com/services/Soap/c/20.0/00D200000000MSH00D20(cut)

Fatal error: Uncaught SoapFault exception: [HTTP] Could not connect to host in (REMOVED HOST NAME)/sfphp/soapclient/SforceBaseClient.php:873 Stack trace: #0 [internal function]: SoapClient->__doRequest('<?xml version="...', 'https://eu0-api...', '', 1, 0) #1 [internal function]: SoapClient->__call('getServerTimest...', Array) #2 (REMOVED HOST NAME)/sfphp/soapclient/SforceBaseClient.php(873): SoapClient->getServerTimestamp() #3 (REMOVED HOST NAME)/index.php(60): SforceBaseClient->getServerTimestamp() #4 {main} thrown in (REMOVED HOST NAME)/sfphp/soapclient/SforceBaseClient.php on line 873