<unknown> means that the current mdw file you are using doesn't have the username in it that owns that object.  It sounds like you aren't using the correct mdw file.

Do a search on your computer for *.mdw files (include system and hidden folders).  There is one named system.mdw that ships with Access - this is one that is used by default for all sessions of Access.  Part of securing a database is to create a new workgroup file for the secure database.  You'd still want the system.mdw for your unsecure databases.

Your search should locate at least two mdw files - system.mdw that ships with Access, and the mdw you created to secure the mdb with.

Open Access and go to Tools, Security, Workgroup Administrator - this will tell you the mdw that is currently set as the default - it should be the system.mdw that ships with Access - if it isn't, then click on Join and join that mdw.  Once you've done this, you should find that you don't need to login to any of your other databases.

Now exit Access and create a desktop shortcut with the following in the target:
"path to msaccess.exe" /wrkgrp "path to secure mdw"

the path to secure mdw is the path to the mdw you created to secure your database.  Use this shortcut when you want to work on your secure database.  The /wrkgrp switch will tell Access to use your secure mdw, rather than the default system.mdw - this is a temporary override of the default for that session of Access only.

Once you launch using this shortcut, create a new database and login as the user that you want to own all the objects in your secure mdb.  Then import all the objects from your secure mdb, and proceed to secure it.  The import will ensure that this user owns the objects.  You can use the Tools, Security, Permissions dialog to :
remove *all* permissions on every object for the Users Group
apply permissions as required to the groups you created.