not able to remove A block from credit note

Hi Experts

user have some invoices which are having A block and for those invoices he created credit notes on which A block continued

now he wants to remove but he is getting error Data Was copied message no.F5343

we tried with FB02, FBL1N mass changes but its not working and we are getting above message i.e. data was copied

Please help in how to remove this A block from credit note.

Thanks

Kartik