Why am I getting the error: "Cannot insert a duplicate key into unique index"?

Hi,

I'm using PostgreSQL 7.3.4 on phpPgAdmin 2.4.2 and I'm getting the following
error when I try and run a SQL query on a script:

Error -
/usr/local/psa/admin/htdocs/domains/databases/phpPgAdmin/db_readdump.php --
Line: 33
PostgreSQL said: ERROR: Cannot insert a duplicate key into unique index
inventory_pkey
Your query:
INSERT INTO "inventory"
("code","quantity","id","description","price","category","image","file","dat
e","uid","sub_type1","sub_type2","sub_type3","title","gst","gauge") VALUES
('1123',NULL,17,'Not really sure what to put in here But I am sure i will
told
:)','17.30',1,NULL,NULL,'2001-01-17',1,'Beans\015\012Means\015\012Hines','',
'','African Mist','0.00',7);

Any idea as to why this is doing this?

Thank you for your help.

Dan