Connection problem

I get a lot of
Error server closed the connection unexpectedly This probably means
the server terminated abnormally before or while processing the
request.

and I think I need some help finding out what is the problem. Any
suggestions on where to start? I think I have maximum logging on
(debug5) but prior to the crash I get no log. I connect to the server
with php/apache and I use pg_pconnect to get persistent connections.

The first log message for a working request to the server says:

LOG: 00000: connection received: host=[local]
LOCATION: BackendInitialize, postmaster.c:2755
DEBUG: 00000: forked new backend, pid=6961 socket=8
LOCATION: BackendStartup, postmaster.c:2581
DEBUG: 00000: received password packet
LOCATION: recv_password_packet, auth.c:940
LOG: 00000: connection authorized: user=myuser database=mydb
LOCATION: BackendInitialize, postmaster.c:2825
DEBUG: 00000: postmaster child[6961]: starting with (
LOCATION: BackendRun, postmaster.c:2925
DEBUG: 00000: postgres
LOCATION: BackendRun, postmaster.c:2928
DEBUG: 00000: -v196608
LOCATION: BackendRun, postmaster.c:2928
DEBUG: 00000: -y
LOCATION: BackendRun, postmaster.c:2928
DEBUG: 00000: mydb
LOCATION: BackendRun, postmaster.c:2928
DEBUG: 00000: )
LOCATION: BackendRun, postmaster.c:2930
DEBUG: 00000: InitPostgres
LOCATION: PostgresMain, postgres.c:3142
DEBUG: 00000: StartTransaction
LOCATION: ShowTransactionState, xact.c:4001
DEBUG: 00000: name: unnamed; blockState: DEFAULT; state:
INPROGR, xid/subid/cid: 8513010/1/0, nestlvl: 1, children: <>
LOCATION: ShowTransactionStateRec, xact.c:4026
DEBUG: 00000: CommitTransaction
LOCATION: ShowTransactionState, xact.c:4001
DEBUG: 00000: name: unnamed; blockState: STARTED; state:
INPROGR, xid/subid/cid: 8513010/1/0, nestlvl: 1, children: <>
LOCATION: ShowTransactionStateRec, xact.c:4026
DEBUG: 00000: StartTransactionCommand
LOCATION: start_xact_command, postgres.c:2200
STATEMENT: SELECT count(*) FROM Users
DEBUG: 00000: StartTransaction
LOCATION: ShowTransactionState, xact.c:4001