i'm really desperate: invalid memory alloc request size 0

Hi,

tonight my database got corruppted. before it worked fine.

since two days i do the following tasks every night

psql -c 'CLUSTER;' $DBNAME
psql -c 'VACUUM FULL ANALYZE;' $DBNAME

before these opertaions i stop all web access. The last months i only did a
"VACUUM ANALYZE" each night and didn't get any failures.

in the morning some sql queries failed. it seems only one table was affected.

i stopped all web access and tried to backup the current database:

pg_dump: ERROR: invalid memory alloc request size 0
pg_dump: SQL command to dump the contents of table "fragentipps" failed:
PQendcopy() failed.
pg_dump: Error message from server: ERROR: invalid memory alloc request size
0
pg_dump: The command was: COPY public.fragentipps (tr_kurzname, mg_name,
fr_id, aw_antworttext) TO stdout;

so i did:
/etc/init.d/postgresql stop
cp -rp /home/postgres/data /home/postgres/datafailure

and i tried to recover from backup which was made just before clustering but i
got
ERROR: index row requires 77768 bytes, maximum size is 8191

is there any chance to get my database keep going again?

pg version is 7.4.2

kind regards
janning