VF31 (billing output) with EDI (6) not working when Invoice item does not start with Item 10

Hi,

We are having a Production High Priority defect.

EDI outputs for invoices (VF31) can not get sent when first  item of invoice is not 10 (e.g. when first item is 20 or 30).

Error message is "VB021 : Invoice Item 000010 does not exist" and message does not get sent.

Any input would be greatly appreciated.

Thanks,

Patrick