exporth physical after creating schematic to make a.brd file.

Hello I'm new in Cadence Allegro, I am trying to export physical after creating my schematic to make a .brd file, but i am encountering error "Schematic supports automatically creating XNets using DML but the Layout will not automatically create any XNets. Change setting in Layout or Schematic, re-generate files, and re-run the flow." Can't import electrical constraint data (pstcmdb.dat)
Somehow i cannot continue making a .brd file. Please someone help me with these. Thank you.