enable 'File Context Menu' after disable

hi.
I read doc of ckfinder:
// If you want to enable it back later, remember in a variable an unlocking function.
var enableAgain = api.disableFileContextMenuOption( 'viewFile', false );
// Enabling back
enableAgain();

Enable 'File Context Menu' don't work after disable . I don't know why so.
Please help me.