Using VBO to change workflow state at cron maintenance

Hi,

I wanted to use a triggered rule with a VBO action to change a workflow state on some contents of a content type depending on the time the action is being executed.
The view works well when I execute it as authenticated user (I must be authenticated with a proper role because corresponding contents are not public).
But, when the action is called at maintenance cron runs, no user is logged and no content can be changed !

I tried to add a prior action to the triggered rule : "Use user object to execute a VBO programmatically" with a preselected user and to select the right option in the argument configuration for the VBO action.
Does anybody know how to solve my problem ?
I harldly hope that someone could help me ...
Thanks in advance.p