Unfortunately, this is an Amazon bug that they have not yet resolved. There is a product in your batch that is causing a conflict with the inbound shipping, but Amazon doesn’t give us any indication as to what the problem item is.
We have reported this issue to Amazon and they are supposed to be working on a fix, however, we have received no updates from them. Luckily, this is a very rare error and we suspect it shouldn’t happen to you again.
In order to fix this issue today, you will need to create and upload a shipment plan file.