I can't seem to move up in the following Lightbike game (copied mostly from this site's version). The game ends when I do, as if I've "crashed" and I'm not sure why. Any help would be much appreciated.

```
:Full
:FnOff
:AxesOff
:0→Xmin:1→ΔX
:0→Ymin:1→ΔY
:ClrDraw
:Vertical Xmin
:Vertical Xmax
:Horizontal Xmin
:Horizontal Xmax
:60→A:92→B
:2→C:2→D:25→G
:Pxl-On(A,B
:Pxl-On(C,D
:Text(-1,28,31,"READY?
:Pause
:For(E,26,36
:Line(29,E,67,E,0
:End
:Repeat G=45 or not(pxl-Test(A,B) and pxl-Test(C,D
:getKey
:If Ans
:Ans→G
:A+(Ans=34)-(Ans=25→A
:B+(G=26)-(G=24→B
:1+pxl-Test(C+1,D
:Ans+(Ans=2 and pxl-Test(C,D-1
:Ans+(Ans=3 and pxl-Test(C-1,D→F
:C+(Ans=1)-(Ans=3→C
:D+(F=4)-(F=2→D
:Pxl-Change(A,B
:Pxl-Change(C,D
:End
:AxesOn
:ZStandard
:ClrDraw
:ClrHome
```