Agent Assignment with Roles / Custom FM Rule

Hi All,

This may have been asked earlier but I could not find a relevant thread so posting it here. Here is the situation. I have a custom rule which returns a Org Unit . Org Unit has some positions/users under it. So I get to a list of users. Now in the standard task I have assigned few roles. If I look at PFCG the users are listed there. But the workitem does not reach the users. Is it because the way standard task is set up? I mean do I have to assign users/org unit rather than task? If thats the case why ? I mean the flow from Org Unit -> User and Role -> User takes me to same user.

When I debugged the agent assignment I see that I get an exception from RH_TASK_AGENT_CHECK FM which says Org Unit is not a valid agent for the task.