>I'm not even sure if the light was the cause but the problem
>does not happen anymore.

Our IBM CE noted this as a potential problem, as excessive light over
the 3494's "skylights" could make barcode reading more difficult for
the robot.  This may be due to strobing, in the laser flickering across
the barcode competing with the AC-driven fluorescent lights.
One wonders about that laser, though, given that supermarket scanners
have no such problems, with lots of fluorescent light overhead.
   Richard Sims, BU