Mapping Flash AS3 object to PHP object

I am using AMFPHP to receive data from PHP in Flash. From PHP I am sending an object having 3 attributes as: username, email and id.In Flash I have created an AS3 VO with same 3 attributes. I am getting the result from PHP when taking the result as a normal object.But when i try to get the result as:

var testVO:TestVO = result as TestVO;

I get the testVO object as null, whereas result has all the data.

Any idea where I might be wrong?