query and pg_dump problem on my postgresql 6.5.3/Redhat 6.2

Help!

A few days ago, my php page began to complain this:
------
Warning: PostgresSQL query failed: pqReadData() -- backend closed the
channel unexpectedly. This probably means the backend terminated abnormally
before or while processing the request.
------

The SQL string in php page is:
------
$sql.='Select news_id,title,summary,publish_time,is_html,if_use_url,url,news_pri ';
$sql.='From newses N,classes C ';
$sql.="Where N.class_id = C.class_id AND C.classname='$class' ";
$sql.='Order by publish_time Desc,news_id Desc Limit '.$Nlimit;
------

NOTE:
I'm on Redhat 6.2 with Postgresql 6.5.3, the database named "news",
and the table is "newses", looks like this (dumped from "pg_dump -s -t newses news"):

CREATE TABLE "newses" (
"news_id" int4 DEFAULT nextval ( '"newses_news_id_seq"' ) NOT NULL,
"title" character varying(100) NOT NULL,
"class_id" int4 NOT NULL,
"summary" text DEFAULT '',
"user_id" int4 NOT NULL,
"url" character varying(100),
"img_url" character varying(100),
"publish_time" date NOT NULL,
"if_show_news" bool DEFAULT bool 'f' NOT NULL,
"if_use_url" bool DEFAULT bool 'f' NOT NULL,
"is_html" bool DEFAULT bool 'f' NOT NULL,
"view_count" int4 DEFAULT 0 NOT NULL,
"news_pri" int4);
CREATE UNIQUE INDEX "newses_pkey" on "newses" using btree ( "news_id"
"int4_ops" );

This table has 243 records, the max news_id is 253.

Later I found queries like these fails in psql:
select news_id,title from newses order by news_id desc limit 10;
select count(news_id) from newses;

But thess works fine:
select * from newses where news_id< 300;
select count(*) from newses where news_id <300;
select count(news_id) from newses where news_id <300;

A simple rule is if I'm running query over the whole
table without condition, I get same error message mentioned above.

I thought my postgresql should be patch or upgrade, so I began to backup the
database on it.

But I found that pg_dump sometimes does not work on that very table,
and sometimes work with a long long time then error.

following are the error message of "pg_dump news -t newses -f newses-data.sql":
------
pqWait() -- connection not open
PQendcopy: resetting connection
SQL query to dump the contents of Table 'newses' did not execute correctly. After we read all the table contents from the backend, PQendcopy() failed. Explanation from backend: ''.
The query was: 'COPY "newses" TO stdout;
'.
------

I read the file(14M) generated and found that after the normally record(91K) there are many character like these:
------
\N \N \N \N \N \N \N \N \N \N \N \N \N
\N \N \N \N \N \N \N \N \N \N \N \N \N
\N \N \N \N \N \N \N \N \N \N \N \N \N
\N \N \N \N \N \N \N \N \N \N \N \N \N
\N \N \N \N \N \N \N \N \N \N \N \N \N
\N \N \N \N \N \N \N \N \N \N \N \N \N
280368896 \N \N 0 \N f f f 0 0
280368896 \N \N 0 \N f f f 0 0
280368896 \N \N 0 \N f f f 0 0
------
And end with
------
\N \N \N \N \N \N \N \N \N \N \N \N \N
\N \N \N \N \N \N \N \N \N \N \N \N \N
\N \N \N \N \N \N \N \N \N \N \N \N \N
\N \N \N \N \N \N \N \N \N \N \N \N \N
\.
------

It is my nightmare now for I can't get back my data. I googled around with
no luck.

Anyone help me to get back the data and tell me what was going on?

　　　　　　　　　　　　　　Yours Wind Wood
　　　　　　　　　　　　　　windwood(at)jingxian(dot)xmu(dot)edu(dot)cn
　　　　　　　　　　　　　　　　　2003-12-04