Lock and pg_stat

- I have a problem with some files on a postgresql 9.0 on windows:

2013-05-10 12:49:08 EDT ERROR: could not stat file "base/773074/30352481": Permission denied
2013-05-10 12:49:08 EDT STATEMENT: SELECT pg_database_size($1) AS size;

I know what does it means: the statistic pooler can`t access the file.
It is a only database server without antivirus (but on a windows cluster machine)

- on disk, the file is shown as a 0-octet file, and there is no security tab when I try to get information.
It looks like this file has been created, opened, and not yet close (or written)

- when I try to get more information on the file with `oid2name` it is unable to give me information:
S:\PostgreSQL\9.0\data\base>"C:\Program Files\PostgreSQL\9.0\bin\oid2name.exe" -
U postgres -d mydb -f 30352481
Password:
From database "lxcal":
Filenode Table Name
----------------------

Certainly because the pg_stat worker can access it, so don`t have info on it?

I tried also:
select * from pg_class where oid=30352481;
but didn't got anything

- This same file is owned by a postgresql backend thread (with `process explorer`) I see that the file is owned by a postgresql --forkbackend with pid 3520
I tried to see what the 3520 process is doing. It is in "<IDLE>"
It is not statistic worker (it is not "postgresql --backcol")

I thought it was maybe a file locked, so I check pg_locks with:

select pg_class.relname, pg_locks.virtualtransaction, pg_locks.mode, pg_locks.granted as "g",
substr(pg_stat_activity.current_query,1,30), pg_stat_activity.query_start,
age(now(),pg_stat_activity.query_start) as "age", pg_stat_activity.procpid
from pg_stat_activity,pg_locks
left outer join pg_class on
(pg_locks.relation = pg_class.oid)
where pg_locks.pid=pg_stat_activity.procpid
order by query_start;

my process (pid 3520) is not listed has having lock.

How can I debug to know what is going on?
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