For some retailers the system send consolidated invoices or ASNs.
When generating this consolidated document the system checks whether the unit price of every item is same for all the invoices. Sometimes there can be invoices which have different prices for the same item, and that fails when consolidating the invoices.
So if you get this error please check whether any invoice has got a different unit price for any item when compared to other invoices and correct it.
Another instance this may occur is when sending credit notes. For certain retailers TOE system do not send credit notes. Sometimes when you create credit notes for invoices, the system fail when checking the Unit prices as the credit note has got a minus value for unit price.
At this point the system raise above error message. If you see this you will have to contact the retailer and send the credit notes manually.
Please contact email@example.com if you have more issues.