Lots of Access errors don't make sense. That's why it's so fun to work with. :O)
Check that you don't have another instance of the database file open. I sometimes do that accidentally. Also check that you do not have a form or a VBA routine with the table as a record source already open.
If all else fails, you might just have a slightly corrupt database. Close it and re-open it. Then compact it and try again. If that doesn't fix it, import everything into a new, blank database and delete the old one.
Bill Mosca
www.thatlldoit.com
http://tech.groups.yahoo.com/group/MS_Access_Professionals