Error during Po Creation "Purchasing group is wrong"

Hi All

Will Creating PO i am getting following error i.e. " Purchasing group is wrong " when i am double click on the error

message it is not showing me any error message following activity i had done

1) Create Purchasing group as "19" (OME4)

2) Assign purchasing group to the material master in MM01

3) Now when i am creating PO it is showing me that line item 10 

Kindly assist what additional config required to maintained  for Fix this error

Thanks

Trinath