How to fix the problem of "archiver process failed"

Hello everyone,

Recently I encountered some problems when using postgres' PITR.
The function worked well before but it starts to get some problems now.

I found out that the postgres archiver did not work properly. It shows
postgres: archiver process failed on 0000000400000007000000FA.

I know this problem results from the missing WAL file in my machine. That
is postgres archiver tries to archive 0000000400000007000000FA but it
cannot find it. However, this is weird because the missing WAL file has
been already copy to my remote backup host.

I would like to know how could this happens and how can I fix this
"archiver process failed" problem. Could anyone give me some comments
please.

Note:
1. The version of the postgres in my machine 8.3
2. This problem happens after I successfully execute the recovery procedure
and try to execute backup procedure.

Best regards,
Leo