Cancel settlement in different year

Hello Experts.

We have a sales order that has been settled during 2012 and part of 2013. Recently we have put a RA key and it doesn´t allow to execute the WIP settlement because of the previous settlements that have been done in the Sales Order.

The system asks me to cancel them but i can´t find the way to do it when they have been settled in a different year from the actual.

Is there any way to do it?

Thanks.

Alex