how to fix my vizard?

[emily800326]

i use the camera to read my ar-code.
but the panel turn black , and i can't see my code.
can someone tell me what the problem.
(when i run another code,also have this problem.)

import viz

viz.go()


ar=viz.add('artoolkit.dle')
camera=ar.addWebCamera()

m0=camera.addMatrixMarker(0,width=50)
modle1=viz.add('box.obj')

links=viz.link(m0,modle1)
modle1.setScale(0.05,0.05,0.05)
modle1.texture('')