You may encounter this warning when 2 grid lines almost meet at a border of the curtain wall or sloped glazing, but not exactly at a point. The curtain panel cannot be displayed.
Warning: There is an invalid curtain panel in the model.
Issue: Typically, this problem occurs in a panel on a sloped glazing. A horizontal and vertical curtain grid on a panel are not meeting exactly at a point, creating a small triangular panel within the main panel; the triangular panel cannot be accurately regenerated because it is too small. This message displays when the program regenerates the curtain panel.
Solution: Cancel the placement and/or the movement of the panel. When dividing the panels in a sloped glazing/wall, it is best to start with the placement of horizontal curtain grids and then snap vertical grids to the horizontal grid. This ensures the grids meet at a point and eliminates the creation of a small panel.