The client determines what gets backed up during an
incremental backup. You can increase the logging level
on the bpbkar process on the client and it will tell
you what is being included and excluded and why. There
are many reasons why you could be seeing files
excluded. I would start with checking the modified
time on the files as previously suggested. You might
also try changing NetBackup from using Archive bits to
using modified time and see if that picks up the
files. This technote also explains about delta time
which NetBackup uses to help determine if an
incremental should back anything up. If the delta time
is less than the frequency of the schedule nothing
will be backed up. You can tell this is the case by
looking at the dt value in the bpbkar log and it will
be 0. This is probably why you are not getting
anything when you are running the incrementals over
and over. Not enough time has elapsed for the dt value
to have changed. 


"A wise man once said 'Wherever you go, there you are'"
      -Mike Brady