Seqno. is not btree?

Hi,
I use Postgresql-7.2.4
I've created following table:

create table vchar (
seqno SERIAL,
col_var character varying (8192)
);

After as many as 2412081 records are inserted, I shutdown my server.
My every record was inserted programatically by :
insert into vchar (col_var) values ('VVV')......(VVV' char sequence was
8192 times long. i.e. in one row 8192 V's are present.)

Next day,I tried the following:
test=# select count(*) from vchar;
count
-------
2568
(1 row)
test=# insert into vchar (col_var) values ('VV');
ERROR: Index vchar_seqno_key is not a btree

What does this error mean? My server log shows 2412081 records inserted
but actual count(*) shows only 2568 records.

Pls. help.
Thx.,
Anagha