http://blog.donews.com/cnsoft/archive/2012/05/03/1582972.aspx

Type 1120: Access of undefined property JSON
无法明确解析多名称引用 JSON

https://github.com/mikechambers/as3corelib/issues/171

If you’re using as3corelib like I’ve been using for quite some time now, you will notice this error. To fix it you simply need to remove the following import (it may vary based on your project structure):

import com.adobe.serialization.json.JSON;

and then you’ll need to modify your code to replace:

JSON.decode(myString);
and
JSON.encode(myObject);

to:

JSON.parse(myString);
and
JSON.stringify(myObject);

You can find the full details of the new implementation of the native JSON support in AS3 on Adobe’s Reference Site

解决办法是移除那个 import 然后把对应的函数名改掉.