Po with acct. assign. u201CAu201D should not accept any numeric except "ASxxx"
Po with acct. assign. u201CAu201D should not accept any numeric material group other than those starting with the 2 digits u201CASxxxxu201D.
For this please use the enhancement to check the material group nomenclature.You can impliment the same by using the Enhancement Spot-ME_PROCESS_PROCDOC for the corresponding Method=CHECK.Here put the required logic so that before saving the PO it will check the same.
Thanks & Regards,