For the snoball game i am developing i am using matrixes for the snoball variables. This allows to create flexible code and to automatize tasks.

I tried to use the same technique with sprites, but DS LUA crashes without explanation

1) sprite loading (works ->balls appear on screen)

   Sprite.LoadPalette( SCREEN_BOTTOM, PALETTE_BALL, "ball1x.pal" )
   BallFrames  = FrameStrip.Create( SCREEN_BOTTOM, 8, 8, "256" )
   BallFrames:LoadBin( "ball1x.raw", 1 )
   ball_spr = {}
   for i = 1,4*BALL_NMAX do
      ball_spr [ i ] = { Sprite.Create( BallFrames, 0, PALETTE_BALL, SCR_XMAX, SCR_YMAX ) }
   end

2)    ball variables are contained in other matrix (works -> verified by printing values on screen)
   ball = {}
   for i = 1,4*BALL_NMAX do
      ball  [ i ] = {player = 0, xpos=SCR_XMAX  ,  ypos=SCR_YMAX, dir=0, on=BALL_OFF  }
   end   

2) But when i try to redraw the sprites the system crashes!
    for i = 1,4*BALL_NMAX do
       ball_spr [ i ]:MoveTo( ball [ i ].xpos, ball [ i ].ypos )
    end

Note: the same ":Move" funtion works fine with sprites that are not values inside a matrix

Any idea of what i do wrong?

Yep, I think Zhen got it.  In step 1, you created a sprite and kept it in a table.  In step 2, you reassign ball_spr to a new table without a sprite.  So, when you try to access the sprite in step 3, it no longer exists.

Thanks,
Waruwaru