vacuum analyze: Tuple is too big (corrupts DB?)

Hello,

when I vacuum analyze my db (6.5.3 on Linux) I cannot access
some data afterwards because the vacuum terminates with

ERROR: Tuple is too big: size 8596

I did pg_dump -o and read in back again, still the same error.

Eg. accessing data after vacuum results in

SELECT envpart_map.*,
envpart_map.oid AS recioid,
member.*,
member.oid AS memoid
WHERE envpart_map.member=member.oid
AND envpart_map.role > 0
AND envpart_map.envelope IN (1072343,1073358,1074472,1073722,14235
82)': pqReadData() -- backend closed the channel unexpectedly.

Where can I get on from here?

Dirk