Rsync not completing - just .xls-files is problem...

My suggestion would be to put the UserMapping file back to the correct location, clear the backup logs, reboot, then run a completely fresh backup but use a different destination folder on your USB drive. That way, all your files will be copied once. Then post any errors that appear in the log after this backup completes. Or if there are no errors, then even better - perhaps your problem is solved.

Also I should ask - do you have more than one user that has saved the same MS Office / excel file? The reason I ask is that I have found that when ms office files are saved first by one user then a second time by a different user, then an ACL is saved. You can actually see the ACL information for a file using the Linux getfacl command. Anyway, on the readynas backup jobs run using either the cp -p command or the rsync -Ava command. Both commands attempt to copy (preserve) file attributes such as ACLs. This always caused errors when copying to a ntfs USB drive in prior versions of Raidiator (<= 4.1.6) because the ntfs driver did not support acls. This should now be fine in 4.1.8 as long as netgear has enabled acl functionality (I'd be surprised if it's not enabled). You probably just need a UserMapping file for this to all start working. Also you should notice that without a UserMapping file all files in your backup end up losing file ownership info and show up as root/root if you do ls -l; but once you create the appropriate UserMapping file all your file ownership and your ACLs will be correctly backed up as well as the content of each file.