Update unit test throws an exception and fails to update

[hatwack]

I got this error and stack trace with a copy of the update sample. I confirmed that the unit test throws the same exception.

PHP Fatal error:  Uncaught SoapFault exception: [sf:INVALID_FIELD] INVALID_FIELD: No such column '' on entity 'Lead'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names. in /mnt/iscsi/www/digitalstreetinc.com/dev/sfconnector/soapclient/SforceBaseClient.php:514
Stack trace:
#0 /mnt/iscsi/www/digitalstreetinc.com/dev/sfconnector/soapclient/SforceBaseClient.php(514): SoapClient->__call('update', Array)
#1 /mnt/iscsi/www/digitalstreetinc.com/dev/sfconnector/soapclient/SforceBaseClient.php(514): SforceSoapClient->update(Object(stdClass))
#2 /mnt/iscsi/www/digitalstreetinc.com/dev/sfconnector/soapclient/SforcePartnerClient.php(171): SforceBaseClient->_update(Object(stdClass))
#3 /mnt/iscsi/www/digitalstreetinc.com/dev/sfconnector/sfconnector.php(34): SforcePartnerClient->update(Array)
#4 /mnt/iscsi/www/digitalstreetinc.com/dev/sfconnector/transmit.php(37): SFConnector->test()
#5 {main}
  thrown in /mnt/iscsi/www/digitalstreetinc.com/dev/sfconnector/soapclient/SforceBaseClient.php on line 514