writepixelfast problems

[CODE]

For particle.particles = Each particles ; draw particles

col = particle\red Shl 16 ; convert to pixel colour
col = col+particle\green Shl 8
col = col+particle\blue

LockBuffer
WritePixelFast(particle\x#,particle\y#,col)
UnlockBuffer

If particle\debris_size > 1
LockBuffer
WritePixelFast(particle\x#+1.0,particle\y#,col)
WritePixelFast(particle\x#,particle\y#+1.0,col)
WritePixelFast(particle\x#+1.0,particle\y#+1.0,col)
UnlockBuffer

If particle\debris_size > 2
LockBuffer
WritePixelFast(particle\x#+2.0,particle\y#,col)
WritePixelFast(particle\x#+2.0,particle\y#+1.0,col)
WritePixelFast(particle\x#,particle\y#+2.0,col)
WritePixelFast(particle\x#+1.0,particle\y#+2.0,col)
WritePixelFast(particle\x#+2.0,particle\y#+2.0,col)
UnlockBuffer
EndIf
EndIf

Next

[/CODE]

Why does this code crash? :(