Hi Reshma,
Are you using the A012 (chief position) relationship in your org. structure? The RH_GET_MANAGER_ASSIGNMENT is only applicable to the head of own org. unit relationship.
This function module finds the organizational unit to which the user is assigned as manager via relationship A012 (is manager of) and this works on the basis of a key date. It only finds organizational units to which the user is 'manager' on the key date or during the period you specified. Please check to make sure the relationships are valid.
Also please use transaction HRAUTH and provide the 2 P_ORGINCON profiles you're referring to so we can view them accurately.
Thanks.