Microsoft.DirectX.Direct3D throws NullReferenceException:
Object reference not set to an instance of an object.
   at Microsoft.DirectX.Direct3D.Texture.GetSurfaceLevel(Int32 level)
   at CodeImp.Bloodmasters.Client.VisualSector.PrepareLightmap()
   at CodeImp.Bloodmasters.Client.Arena.PrepareRendering()
   at CodeImp.Bloodmasters.Client.General.DoOneFrame(Boolean process, Boolean render, Boolean renderhud)
   at CodeImp.Bloodmasters.Client.General.GeneralLoop()
   at CodeImp.Bloodmasters.Client.General.StartGame()
   at CodeImp.Bloodmasters.Client.General._Main(String[] args)
   at CodeImp.Bloodmasters.Client.General.Main(String[] args)

I was alttabbed out of BM when I heard chirping noises, you were changing the map maybe?  It then crashed when i tried to tab back in.