HABTM Duplicate entry error

I have a model OrderUser and a model Venue, both are related through a
HABTM to relationship and the join table is order_users_venues with
the two foreign keys venue_id and order_user_id. I am trying to add
venues to a user, it works fine if one user is doing this, but if
another is it reinserts the same ids into the table and screws
everything up:

Mysql::Error: Duplicate entry ‘1’ for key 1: INSERT INTO
order_users_venues (venue_id, id, order_user_id) VALUES (1, 1,
2)

This ‘1’ is entry 3 in the table.

Obviously I am not using HABTM correctly or am using it when it I
shouldn’t be.

Please advise!

Thanks,
John

Problem is solved!

FYI - in the migrations

create_table :tablename, :id => false

:id => false being the key there