I would like to first ask if you are able to provide the Application those reports were created in, as well as the type of report (ie. Actual Hours Report in Projects/Workspaces or whichever type of report and application is correct)?
Also, can you attach screen shots of the details page of each of the two reports so we can see if any of the filtering is causing the discrepancy in the hours you are seeing?
These additional details and screen shots will help us in getting a more definite answer for your reporting problem.
Thank you in advance for whatever you can provide. If you have any questions please let me know.