The entity name must immediately follow the '&' in the entity reference.
在flex中出现上述错误，是因为不识别&标识符，需要将：

<mx:TextInput text="{(_feed.url && !_feed.isTemporary)?_feed.url:'Save Feed to generate URL'}" 

改成

<mx:TextInput text="{(_feed.url && !_feed.isTemporary)?_feed.url:'Save Feed to generate URL'}" /

原文见：http://www.markledford.com/blog/2008/01/30/the-entity-name-must-immediately-follow-the-in-the-entity-reference/