Cannot change batch number

Hi,

In AX 2012, I have a purchase order which is derived from a planned purchase order. When I try to change the batch group on the purchase order line, I got the error "There are transactions with status Reserved ordered for the dimension of item 12411. Consequently inventory dimension cannot be changed."

But for that item the batch group is mandatory, otherwise I can post the product receipt.

What can I do now?

Thanks,