ILIAS Developers: Webservice login Internal Server Error

Trying to use 

http://[DOMAIN]/webservice/soap/server.php

Returned:

WSDLSOAP-ERROR: Parsing WSDL: Couldn't load from 'http://[DOMAIN]/webservice/soap/nusoapserver.php?wsdl' : failed to load external entity "http://[DOMAIN]/webservice/soap/nusoapserver.php?wsdl"

Trying to use

http://[DOMAIN]/webservice/soap/nusoapserver.php

Returned:

Notice: Undefined index: _transient in /[OMITTED]/webservice/soap/lib/nusoap.php on line 77
Fatal error: Uncaught Error: Class 'ilContext' not found in /[OMITTED]/webservice/soap/classes/class.ilSoapAdministration.php:190 Stack trace: #0 /[OMITTED]/webservice/soap/classes/class.ilSoapUserAdministration.php(58): ilSoapAdministration->initIlias() #1 /[OMITTED]/webservice/soap/include/inc.soap_functions.php(45): ilSoapUserAdministration->login('[OMITTED]', '[OMITTED]', '[OMITTED]') #2 /[OMITTED]/webservice/soap/lib/nusoap.php(4014): ilSoapFunctions::login('[OMITTED]', '[OMITTED]', '[OMITTED]') #3 /[OMITTED]/webservice/soap/lib/nusoap.php(3695): nusoap_server->invoke_method() #4 /[OMITTED]/webservice/soap/classes/class.ilNusoapUserAdministrationAdapter.php(70): nusoap_server->service('<x:Envelope xml...') #5 /[OMITTED]/webservice/soap/nusoapserver.php(49): ilNusoapUserAdministrationAdapter->start() #6 {main} thrown in /[OMITTED]/webservice/soap/classes/class.ilSoapAdministration.php on line 190

PHP: 7.0.22

OS: Ubuntu 16.04

Any ideas?