drop constraint primary key

project=# select version();                          version
-------------------------------------------------------------PostgreSQL 7.2.1 on i686-pc-linux-gnu, compiled by GCC
2.96
(1 row)

Running above, am trying to drop the primary key, but get the follwing
error.

project=# alter table class_teacher_rlt drop constraint
class_teacher_rlt_pkey restrict;
ERROR:  ALTER TABLE / DROP CONSTRAINT: class_teacher_rlt_pkey does not exist

project=# \d class_teacher_rlt                         Table "class_teacher_rlt"       Column        |           Type
       |         Modifiers
 
----------------------+--------------------------+--------------------------
--class_id             | integer                  | not nulluser_id              | integer                  | not
nullschool_id           | integer                  | not nullstart_date           | timestamp with time zone | not null
defaultnow()end_date             | timestamp with time zone |class_action_type_id | integer                  | not null
default1action_detail        | character varying(100)   |teacher_role_id      | integer
|ind_prim_teacher    | boolean                  | not null default
 
'f'::boolind_lead_teacher     | boolean                  | default 'f'status_id            | integer                  |
default1created_date         | timestamp with time zone | not null default 'now'last_modified        | timestamp with
timezone |
 
Primary key: class_teacher_rlt_pkey

Any ideas?

Thanks.

Marie