Re: "Context does not exist" error

@lilian

    You are missing an array in your paramters forming line 

$enrolment = array(
'roleid' => 5,
'userid' => 24,
'courseid' => 69
);
$enrolments = array( $enrolment );
$params = array( 'enrolments' => $enrolments );

it should be 

$enrolments = array( array($enrolment ));

Note that a tool to generate proper imbrication of parameters for all WS calls has been submitted here

http://tracker.moodle.org/browse/CONTRIB-3472

Cheers

;