Entry not found in index

Dear Allwe have 2 servers clusterd and there is replication between the two servers , we run domino 6.5.3 under windows and I recive this message daily many times ,

the message >>>>

Unable to store document in LOOPBACK “Server Name” mail\UsrrMailDB.nsf (NoteID = 4890) from mail\UsrrMailDB.nsf (NoteID = 4890): Entry not found in index on remote server

and another message >>>>

Partially replicated LOOPBACK “Server Name” mail\UsrrMailDB.nsf (due to previously reported error)

end >>>>>>>>

please note that the database and the user are exist on both server and the server has Manager on evrey database

Help Please