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