It would be too costly in terms of disk space to duplicate all material data from the props.dbs file into every simulation file. Therefore a simulation file only retains the information on materials referenced by material model selection. This information includes:
To make data of other materials available, STAR-CCM+ accesses the props.dbs file directly. This is the case when, for example, you want to replace a selected material.
That is why the props.dbs file must be in its normal place (the star subdirectory of your STAR-CCM+ installation directory) when you start a new simulation, or when you open an existing simulation and intend to replace materials.
Additionally, if multiple databases were used in creating a simulation, all of those databases must be in the places they occupied when they were loaded into the simulation, otherwise any unique data they may contain will not be accessible within the simulation unless you load them again.