Call to soapclient_init_client produces 'Undefined Variable: $url' error

Please forgive me if my PHP-ignorance is the reason for this behavior, but when I'm initializing a NuSoap/WSDL client, I get several errors starting with the use of $url in $cache->get($url); (soapclient.module line 534). Here is my code:

$options = array();
$options['use'] = 'literal';
$options['style'] = 'document';

$result = soapclient_init_client(
'http://www.sample.com/sampleservice.asmx?WSDL',
TRUE,
$options);

The remaining errors are fopen() sort of things that may be related to my platform or configuration, but this first one seems unavoidable.

Thanks!

James