NuSOAP for PHP 5 modifies the NuSOAP library so that it doesn't have a class name conflict with the PHP5 soap extension.

NuSOAP's class name is 'soapclient'. PHP5 includes a SOAP extension whose class name is also 'soapclient'. As a result, you effectively can't use NuSOAP with PHP5. NuSOAP for PHP5 simply changes the class name to 'soapclientnusoap'.