Hi Kumar,
Are you sure you created condition records with same amount (24.50) for 3 difference periods?
It doesn't make sense.
The only possibility that duplicated KNUMH occurs in standard system is described in note 66943.
This means you first created a condition record with amount 24.50 from 05/13/2014 to 31/12/9999.
Then you inserted a condition record with a different amount 25.00 from 04/03/2015 to 04/31/2015.
In this case, the first and third condition record have the same number. This is standard behavior.
Best regards,
Tao