Back up first!!!

You should be able to just add it in.  No special considerations.
Try it on a copy just in case it doesn't behave the way you expect.

Be aware that any relationships you have may be affected.  
Make the changes and test it out.  Let us know if you have issues.

I received the following error msg "file sharing lock count exceeded"
And thanx

Gail are you trying to do this in a split db?

You would have to open your back end directly.  
The same would apply if you are in a MulitUser db.
You may have to open it in exclusive mode.  See Open Database Exclusively

Please don't double post.  Duplicate post deleted.  

Did you try the suggestions above?

yes & it did not work.

You could add a temporary button to loop through all the tables in your database and add the ID field if it doesn't already exist.
As Scott said above - BACK UP your database first.

I would just manually add the primary keys (autonumbers) where needed. The tricky part is going to be properly setting up all of your relationships by replacing your existing keys. See Replace Natural Key