For example adding blank lines as separators for hosts may lead to file corruption and the file cannot be parsed anymore. Which result in clients not being available:
[Major] From: BSM@myserver "mybackup" Time: 10/06/2016 13:00:00
[61:2021] Host myclient is not in this cell.
Object will not be backed up.
In general, clients need to be added to cell_info using the Data Protector Graphical User Interface to ensure there are no corruptions in the file.