Hi,
I believe the upper part is not for a counting document as created from the QIE (whereas I am not sure how the process to use this tab at all looks like). And if you can not edit, restart the transaction and click in the field with the quantity in the lower part, it should then be editable. somehow this field is a bit ... sensible.... After entering the counted quantity the field for the exception code will appear.
Brgds
Juergen