I have a project that includes several structures and several column grids. A hardware glitch caused OpenBuildings Designer to crash, and after restarting the software the Grid Systems dialog displays a list of grids but none of their graphics display in the preview window, nor do they display when using the Set Active Grids tool from the Floor Selector toolbox.
Since Grid data is stored in the BB_FloorMaster.dgnlib file, it is best to rename the file currently in your workset's \dgnlib folder and copy your most recent backup version over to that same location in order to restore the missing Grid geometry.