add primary key doesn't block?

Hi,

I'm testing the migration procedure for a client, we want to migrate
from 8.3.6 to 8.4

When we perform a test migration of the data we found some errors on
the logs, one of them is this one:

"""
mic=3D# ALTER TABLE tcom_invitacion ADD primary key (id_invitacion);
NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index
"tcom_invitacion_pkey" for table "tcom_invitacion"
ERROR:  concurrent insert in progress
"""

actually, no indexes were created on this table...
and when i tried to add the PK manually after migration i get this
same error (not always, it seems this time the index is being created
but this time i did it inside a transaction)...

doesn't the index creation of the index block the table so, that
message should not appear?

--=20
Atentamente,
Jaime Casanova
Soporte y capacitaci=C3=B3n de PostgreSQL
Asesor=C3=ADa y desarrollo de sistemas
Guayaquil - Ecuador
Cel. +59387171157