Table extension is not working in Ax 2012 R3

I have created table extension for InventJournalTrans by using Serialization process.

When I tried to pack the table it is not working. 


This is the code I'm using to pack the table.

select Recid from inventJournalTrans
       where inventJournalTrans.RecId == _inventJournalTransRecid;

inventJournalTransExt = inventJournalTrans.inventJournalTransExt();
inventJournalTransExt.SendToWMS = Noyes::Yes;


Please correct where I am doing wrong.

Thanks in advance.