MemoryContextAllc error.

i was trying to back up db from the server.
i found the error while i was trying to backup.

bash$ /usr/local/pgsql/bin/pg_dumpall > db.out

ERROR:  MemoryContextAlloc: invalid request size 4294967293

PQendcopy: resetting connection

SQL query to dump the contents of Table 't_oommain' did not execute correct=
ly.  After we read all the table contents from the backend, PQendcopy() fai=
led.  Explanation from backend: 'ERROR:  MemoryContextAlloc: invalid reques=
t size 4294967293

'.

The query was: 'COPY "t_oommain" TO stdout;

'.

pg_dump failed on xenodb, exiting

what shall i do here?
please give me the solution for this problem.
Thank you very much.=