In the version 1.1.3 yii CAutoComplete was deprecated, so for better result you should consider using CJuiAutoComplete to make autocomplete in yii framework.
To use this widget is more easy to use but with the multiple selections of CJuiAutoComplete maybe you should have to implements more javascript functions.
Let's take a look how to make CJuiAutoComplete with multiple selection enabled. Assume you have code in the article in views article /protected/views/article/_form.php. And I have table with just only 2 fields : id_tag and name