meeting requests sent to a user gets sent to another outlook user

user A sends meeting request to user B, user C(in a different department) gets the meeting request even though she was not invited. This only happened when meeting request is sent to user B
Problem was fixed by having user A close outlook, re-open Outlook by typing
start, run, Outlook /Cleanrules, close outlook and run Outlook /cleanfreebusy
This fixed the problem. User C no longer received meeting requests sent to User B