Try nsrxchrc.exe -s sibhqfiles01 -t "Fri 23 feb 15:00:09 2007" MSEXCH:MB/mailbox_name_here

You should run this from EXCH server and just replace mailbox_name_here with mailbox name.

Have you performed brick level backup too? nsrxchrc usage is:

[-D diagnostic_level] [-h alternate_date] [-I input_file]
[-k alternate_pass_phrase] [-p temp_dir]
[-s NetWorker_server_name] [-t browse_time] save_set1
[save_set2 save_set3 ...]

See table 16 for MB saveset format (but only if you did brick level backup).

Also, you really wish to put 7.2.2 jumbo patch if you are running initial 7.2 (even that is not related).

I do a backup with the command : MSEXCH:MB, i have already read the admin guide for the exchange but i didn't find the good argument for the save_set.
my version of networker is : 7.2.2 Build 422.

Do you have log from backup which shows it has been saved?

Sorry but it's doesn't work, always the same message

This folder has never been saved, and so cannot be recovered: /Private Mailboxes/EBM001/Inbox/Monitoring/
[252] 02/23/07 16:03:10 rcmain(882): begin_mb_item_recover failed with status = 0x00000011

Yes i have the log but we only see for each mailbox the name and the size :

[5724] 02/27/07 09:49:28 Success: Deged Frertic 29 MB 862654 bytes/second
[5724] 02/27/07 09:57:42 Success: Dgland Jean-Phippe 946 MB 1962030 bytes/second
[5724] 02/27/07 09:57:49 Success: Digruer Narc 2944 KB 425919 bytes/second

Try support - either something is wrong with syntax you use or you might have corruption within EXCH database.