Strange Ray in Interior by Vray plane light

Hi all,
I don’t know if this thread is for here, but i want to ask you if somebody knows from where could the problem come…

As you see there is a very strange light trace on the walls…Exactly parallel to a V-ray plane light which is One sided, Invisible and at the right and behind from the camera position…
If i make this light V-ray dome, or Sphere - the problem is decided. Is that the only one suggestion?
Thanks to all in advance.

If you wish, you can send this to vlado@chaosgroup.com (maybe just the walls and the light), since it’s hard to tell what may be causing it just from the image.

Best regards,
Vlado