1 model rendered 2 times?

Remember and set the cameraclsmode back to default after the last render, to clear the screen. Then set it afterwards back to

CameraClsMode cam,0,1

So it becomes:

Graphics3D 640,480,0,2
SetBuffer BackBuffer()

cam=CreateCamera()
box=CreateCube()
base=90

While Not KeyDown(1)

base=base+1 : If base>360 Then base=base-360
x#=0+Cos(base)

PositionEntity box,x,0,5
CameraClsMode cam,1,1
RenderWorld

PositionEntity box,x,4,5
CameraClsMode cam,0,1
RenderWorld

Flip
Cls

Wend