Extened Rebate Ageement - VB(D

Hi Gurus,

I need to extended the rebate agreements to new period.

we can do this by two way.

1. VB(D
2. VBO2 -> Extras-> Extended Agreements.
   

I have maintain the Agreement Calendar as Z1 in Config. which settlement date as end of the month. I have assigned this Agreement calendar to my rebate agreement type in SPRO.

when i try to create the Extended Agreement, system shows the current validity period  and the rebate agreement validity period as the same and no new Rebate Agreements created.

Please let me know how functionality of extending rebate agreement works?