Are you in a multi-site environment? If so, make sure that the site indicated on the order release matches the site you’re trying to ship from. The other thing to check would be whether the line is marked as a Buy to Order but isn’t linked to a PO.
I’m not sure what was wrong with it. However, our CFO was able to get it to ship by doing New Line instead of Mass Shipment. We’re still not sure why it showed as already shipped but this got it out.