Vista - Ntbackup failure

Hi, We have ntbackup configured in a server with Windows 2003 server std. It
was working fine, but now we are having problems. The job summary is as
follows:
"Normal backup. full log. do not verify. Use hardware compression. do not
restrict acces to owner or administrator
some file types excluded replace data on media use media name 'Daily' Use
set description 'Daily' "
Some days the log shows that the data was not replaced in the tape, other
days, the backup copy to the temporary location is not succesfully done.
However, the log does not show this as an error, it simply does not do the
tasks it is supposed to do. The system operator is the one who notices the
failure. Could you please give us advice about this inconvenient?
Besides from this, is there any way to edit the job?
Thanks in advance

Maria