Changing Dunning Procedure for Item that was dunn already

Hello,

Our customer wants to change the dunning procedure of the items From S1 to R1.

The items were already dunn in the past:

Date                            Dunning Procedure      Dunning Level

01/01/2010                   R1                                01

01/04/2010                   R1                                02

01/06/2010                   R1                                03

01/01/2011                   S1                                01

Now when I change the dunning procedure of the items from S1 to R1 and run the fpva I'm getting Dunnin g procedure: R1 and dunning level 02 although I want to dunn the item from the beginning so I want it to strat from R1 and dunning level 01.

What can I do ?

Thanks,

Vered