I fix it as I transfer all my drawings to another new Archicad page with Command_Copy. However, sometimesarchicad still dont react for the changes I did in ToolSettings(Ctrl+T). I dont know why.. I'll carry on & inform you.. Thanks a lot..

Thanks a lot sir, I have fixed the problem with your mentorship. However, I recognize that I couldnt modify any option with Ctrl+T_ToolSettingsForStairs, If I wanna change anything. My solution works on only redraw stair from scratch. I have an another modifiying problem wit...

Thanks for replying, Unfortunately, my problem isnt underside of the stairs, my problem is undefined volids in my stair in 3d. There is a mass but its unseen on there. The blue contour line define all solidity for stair, but in 3d I cant see there (only void btw slab&stair) ...