If you attempting to ship an order where the only item left to be fulfilled is currently on Back order, it will not work.
If any of the address information is not complete, the integration will not work.
If the Location and warehouse location on the items do not match it will not work.
If the item does not have weights and measurements it will not work.
You will need to Edit the Sales Order, change the line item which is on Back Order from 'Do Not Commit' to 'Available Quantity' and then set the status of the Sales Order to 'SigLoch Ready to Print'
This will allow the order to progress over to SigLoch.