Create index problem ( _bt_sort )

Hello,

When i try to create a index (btree on text field) after a restore i've
the
following error :
FATAL 1: btree: failed to add item to the page in _bt_sort (2)

But , if i had some rows on this table , the index creation works fine !

The table contains 1 million rows.
I've tried a lot of time , on postgresql 7.0.2 and 6.5.3

Any idea , thanks

raslog=# select count(username) from log2000 ;
count
--------
965047
(1 row)

raslog=# create index user2000 on log2000(username);
FATAL 1: btree: failed to add item to the page in _bt_sort (2)
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
raslog=# insert into log2000 select * from log2001 ;
INSERT 0 111729
raslog=# create index user2000 on log2000(username);
CREATE
raslog=#

--
Loïc TREGOUËT