duplicate key

hi,

medias=> insert into medias (name, location) values ('BLABLA',
'Montreal');
ERROR: Cannot insert a duplicate key into a unique index

Here's my database & tables :

Database = medias
+------------------+----------------------------------+----------+
| Owner | Relation | Type |
+------------------+----------------------------------+----------+
| postgres | medias | table |
| postgres | medias_media_id_key | index |
| postgres | medias_media_id_seq | sequence |
+------------------+----------------------------------+----------+

Table = medias
+----------------------------------+----------------------------------+-------+
| Field | Type | Length|
+----------------------------------+----------------------------------+-------+
| media_id | int4 not null default nextval('"
| 4 |
| name | text not null
| var |
| location | text
| var |
+----------------------------------+----------------------------------+-------+

I don't specify a value to media_id, so why i got this error? It's
supposed to increment by itself (media_id serial). But, i have to say
that i import the data in medias with the function copy from... i import
also media_id information. Maybe now, i cannot add because my
medias_media_id_seq do not correspond to my new "importation". How can I
fix that?

Thank you very very much and once again sorry for my english.
Patrick