Table privileges

Hi, I have not done this before. I am trying to revoke all rights from public on specific tables and then to grant select rights only, but for some reason the privileges stay active (are not revoked) on these tables - "revoke all on <tabname> from public" "grant select on <tabname> to public" The commands are executed successfully, but when I do a table info in dbaccess afterwards, "public" still has full table rights - update, insert, delete, etc. I also tried revoking these rights individually - "revoke update on <tabname> from public" but this crashes on - 580: Cannot revoke permission. 111: ISAM error: no record found. How can I get around all this ?