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