使用niceditor拓展时出现问题，求助 [ 新手入门 ]

CException
Alias "ext.niceditor.nicEditorWidget" is invalid. Make sure it points to an existing PHP file and the file is readable.

我按照拓展用法那样写，但报错，不知道哪错了？

$this->widget('ext.niceditor.nicEditorWidget',array(
	"model"=>$model,                // Data-Model
	"attribute"=>$model->content,        // Attribute in the Data-Model
	"defaultValue"=>'defaultValue text here',
	"config"=>array("maxHeight"=>"200px"),
	"width"=>"400px",       // Optional default to 100%
	"height"=>"200px",      // Optional default to 150px
));