Problem in taking the database dump

Hi,

   I am facing a strange problem while taking dump of a postgres
database using pg_dump.
whenever I start the pg_dump command to take the backup of that
particular database, it stops within few minutes with the below
mentioned error:

*[root@s8-msd-2 bin]# ./pg_dump -Upostgres pdc_uima_dummy >
/hdd2-1/pdc_uima_dummy_108_18092012.sql
pg_dump: SQL command failed
pg_dump: Error message from server: ERROR:  invalid memory alloc request
size 18446744073709551613
pg_dump: The command was: COPY public.object_data (id, wkb_geometry,
obj_type_id, obj_beginoffset, obj_endoffset, source_id, sentence_id,
last_mod_date, obj_norm_value, obj_text, entity_name, frequency) TO
stdout;*

After repeating the process many times I am getting the same error every
time.
Due  to space problem in the database server, the tablespace of that
particular database is mounted on  another  storage server. Is this
mounting is the cause of the error or anything else? Plz suggest.

Thanks & Regards,
Himanshu Joshi