Invalid Page Header - Mailing list pgsql-admin

Hi everybody,
    I have a Postgres Database Server  8.0 in a Windows 2000 Professional.

    I need to migrate this server to 8.1.4 or 8.1.5 Posgresql Version, but, when I execute backup command from pgAdmin
IIIor from a command line (pg_dump [parameters] ) I get this error: 

        invalid page header in block 4686 of relation "tb_Bilhete"

Details:
==========================
pg_dump: ERROR:  invalid page header in block 4686 of relation "tb_Bilhete"
pg_dump: SQL command to dump the contents of table "tb_Bilhete" failed: PQendcopy() failed.
pg_dump: Error message from server: ERROR:  invalid page header in block 4686 of relation "tb_Bilhete"
pg_dump: The command was: COPY public."tb_Bilhete" ("inIdBilhete", "dtDataHora", "inDuracao", "vcNumRefPrivado",
"vcNumRefPublico","vcNumPartPrivado", "vcNumPartPublico", "chDirecaoRef", "vcTronco", "chInterno", "chProcessado") TO
stdout;
pg_dump: *** aborted because of error
Process returned exit code 1.
==========================

How Can I resolve this problem?
I have other backup, but I need the more recent backup.

I search at the internet about this problem, but I find solutions only for Linux System using Linux tools.

Thanks
André Guergolet