I have used "is not valid" in the action and set the action as " Manager is not valid" . But when the condition is met, the Manager field is assigned with "unassigned" value. I do not have other rules, which use default to "unassigned".
Still for the records satisfying the condition, i see that the value of Manager column for those records is becoming "unassigned".
I do not want the manager value to be reset to unassigned. I just want the validation failure to be reported over mail.