[help] Blitz3D programming question

Hi everyone, I've used Blitz3D for about just 2 days yet, and I'm creating a 3d tool, but am getting 1 error and having 1 problem; - "Memory access violation (just when the program runs for about 2 minutes or something, no matter WHAT I do while running my "program")" - When it should count the surfaces of the box just created, it counts 0 surfaces... First about the surfaces, this part counts and shows the amount of surfaces (which says it's 0 surfaces, which isn't true...(should be 1 or so))

...
While Not KeyDown(1)
...
;creates the box when the user clicks on the screen
If mode$="CreateCube" Then 


      If MouseHit(1) > 0 Then 
	  Boxes = Boxes + 1
      Cube(Boxes) = CreateCube()
      cube_x = MouseX()/factor#
      cube_y = MouseY()/factor2
      PositionEntity Cube(boxes),cube_x,1,5
      TurnEntity Cube(boxes),0,60,0
      CubeSurfaces(Boxes) = CountSurfaces(Cube(Boxes))
      mode$ = "ScaleCube"
      EndIf 


EndIf
...
RenderWorld 
;shows the amount of surfaces of the created box(es)
For am = 0 To boxes
 If am > 0 Then Text 0,am*10,"Box"+am+":"+CubeSurfaces(am)+" Surfaces, x vertices, x polygons"
Next

So what could be wrong with this? And the Memory access violation error I get from this part:

button9 = LoadImage( "C:\Documents and Settings\JDB\Mijn documenten\Skyfes Modeling Tool\button9.bmp" )
MaskImage button9,0,0,0
DrawImage button9,850,240

but first I got it from another loadimage, very strange since all the buttons it loads in the same way and are all .bmp, but only with 1 button I'm getting this error each time... SO what's/could be, wrong? Thanks in advance! Skyfe.