If you are unable to post a packing job due to the error 'There is no Default Store against the Source part' then you will need to add a Default Store to the part code which is defined in the following location:
From the Toolbar select Stock Control
Then select Parts
Find the Source Part Code
Select the Location tab
On the All Subtab populate the Default Store
Once done, return to the Packaging Job and right click and Post. This should post without issue.