ERROR: Unable to locate type oid 0 in catalog...

hi all,
we currently experience an original problem
on a production server with a postgresql 7.1.3
( a bit old, I know :\ )

We just want to know if somebody experienced this problem:

the error message :

"ERROR: Unable to locate type oid 0 in catalog"

I know that such a type can't exists as the types are
generated at the install with the first oid "16".

We found that drop the table en re-creating it with the same data
fixed the problem...

We think about a hardware problem (RAM default or disk maybe)
occurred and killed parts of our data.

These queries worked last week, we got many other problems too
during the last week on
"operators = from typeX to typeY"
disapeared
(fixed by creating these operators in the emergency)

Next to this, we can now see pg_temp.<num>.0 tables appearing in the
\d output !?

this looks like temporary tables "getting to public" ?

oid | relname
1048844570 | pg_temp.20806.1
1048844234 | pg_temp.20806.0

We stongly think about upgrading, but these problems
drops pg_dump to a fatal error... (Murphy's my best friend :] )
so do backups for a few days :(

I don't ask for a quick fix,
but just something like: "drop all that and upgrade"
or "do that at last..."

best regards,

franck