Also, do you see those dbs via nsrinfo? I believe we recently had a thread on subject how to do that exactly.

Thank you your return and thank you again for the microsoft link. I understood the messages about skipping. There is more in question:
These are the return from this backup group.

[3364] 07/25/06 10:24:45 Backing up of master succeeded.
[3364] 07/25/06 10:24:47 Backing up of model succeeded.
[3364] 07/25/06 10:24:48 Backing up of msdb succeeded.
[3364] 07/25/06 10:24:50 Backing up of pubs succeeded.

3364] 07/25/06 10:24:51 Skip building named instance directory because there are no named instances installed or running on this machine.

But there are more databases that doesn´t appear inside the log. Do you know if there´s a limit for the displayed succeeded databases (only 4)?

Do you always see same databases missing? If yes, what happens when you try manul client initiated backup from the client of those missing?