a simple toolbar configuration

using jQuery plugin, and a newbie in CKEditor (not in jQuery)...

if I use:

$('textarea#greeting-text').ckeditor({
    toolbarGroups: [ { name: 'basicstyles', groups: ['basicstyles', 'cleanup'] } ]
});

every thing goes ok, but if I want to hide some buttons and use:

$('textarea#greeting-text').ckeditor({
    toolbarGroups: [ { name: 'basicstyles', groups: ['basicstyles', 'cleanup'], items: ['Bold', 'Italic', 'Underline', '-', 'RemoveFormat'] } ]
});

or even without the group part, I get:

Uncaught TypeError: Object Bold has no method 'render'

what am I missing?