I'm trying to open a map with db 2 and got two error messages and the level does not open. This from doom builder:   Unable to build the nodes: The nodebuilder failed to build the expected  data structures. The map will be saved without the nodes.   Second one from PrBoom+:   P_SetupLevel: Level wad structute is incomplete. There is no ML_SSECTORS lump.   Someone know how eventually solve this ?