Im sorry I have read this through a few times and am confused what precisely you are tying to acheive.
You have said the following
When I attempt to use to API to get the content of an item I found in the archive ( I am able to list the documents contained in the archive) I get that COM error.
What are you trying to use, search, archive explorer, Outlook, OWA????
Anyone has an idea if there could be an issue because of the way the domains are setup or why the Admin Console would turn up those squares?
No idea what you mean by squares??
You use the Admin Console as the prodcution user? Not sure what that would prove?
Think that you will need more help than people will be able to give you on the forums to be honest. It sounds at best as if the reason you get access is denied is rendering the content back to the production domain, but there is so much it could be impossible to say from a few lines on forums.
Not sure how much EV expereince you have but it is a complex product and add to this the complexitiy of multiple domains etc in my expereince you need assistance from Professional Services Symantec or otherwise to set up this kind of non out the box config, if there is such a thing.