Is 'Group' one of the fields that gets reported? If so you will get multiple lines for a single individual, one for every group they are a member of. Eliminating that field from the report, may eliminate the duplicate lines you are seeing.
Thanks for the reply...yes I do have groups as one of the filters.
Based on your suggestion, I re-ran the report...and located individuals with duplicate entries...and then checked their group memberships. As it turns out the ones I checked were all only members of the one group that I had included into the report.
As a test I re-ran the report and removed the group filter...and still got the blank lines.
Any other thoughts?
I would see if there was any other field that generates duplicate fields. If that doesn't solve the problem, then I would pull the report from a different location. If you pulled the Reports section of the Course, then I would go to the Reports tab and generate the report from there and see if that made a difference.