Stability questions RE 6.5 and 6.3.2 & 6.3.2 problems

This is an error I am getting with 6.3.2
under freebsd 2.2.8
Mon Sep 6 16:44:48 BST 1999: NOTICE: SIAssignBackendId: discarding tag 2147483020
Mon Sep 6 16:44:48 BST 1999: FATAL 1: Backend cache invalidation initialization failed

Our database is about 38megabyes. We do have about 20 - 30 simultaneous connections. Most accessing the same
tables with transactions.

We see the above error quite often, and once it happens we have to restart postgress and our application.
We are accessing the db via jdbc.

We do not use any large objects (since they caused constant backend crashes for us)

1) Can anyone explain what this error is, and if there is something we can do to work around it.

2) is 6.5 stable enough for 23.5x7 production applications.

3) are large objects stable in 6.5 (where I can store and access 20,000 of them regularily)

4) if all my sql works in 6.3.2 will it need any changes to run under 6.5

I am loosing the -- flush this free crap and move to oracle -- war here, so please help.