Every project must have the project Floor Manager data stored in it's own dgnlib.
The default name of the Floor Manager dgnlib is BB_FloorMaster.dgnlib, located by default in the project dataset. For instance in the delivered GB Dataset the location is "C:\ProgramData\Bentley\AECOsimBuildingDesigner V8i Ss6\WorkSpace\BuildingDatasets\Dataset_GB\dgnlib\BB_FloorMaster.dgnlib".
The location and name of the dgnlib is defined by BB_FLOORMASTER_DGN in each Project Configuration File (PCF).
The data contained in BB_FloorMaster.dgnlib is obviously very important, you may wish to be able to name each project's floor master with a unique name to avoid any mixup in operation and when archiving or restoring from backup.
Provided that the filename specified by BB_FLOORMASTER_DGN matches the actual dgnlib name it will be found correctly.
If you have a small number of projects simply editing the BB_FLOORMASTER_DGN statement in each project's PCF will be a valid approach.
For larger numbers of projects (or if you like me you just don't like repetitive tasks!) try the following method to add a project code to your configuration and use that to specify individual names for the Floor manager dgnlib: