Error in spawning a dbus-launch - what is that? [closed]

I like to run a cron that snapshots a cam like this:

* 9-17 * * 1-5 vlc -I dummy v4l2:///dev/video0 --video-filter scene --no-audio --scene-path /home/foo/tmp/cam --scene-prefix snapshot --scene-format png vlc://quit --run-time=1

But when the cron runs it just throws an error I don't understand:

** Message:Failed to get session bus:Error spawning command line 'dbus-launch --autolaunch=55644972b3c91c1d24d83d8252721f00 --binary-syntax --close-stderr':Child process exited with code 1

In the web I find no clean or good documentation what that is. Can you help me figure it out?