While shipping ChannelGrabber orders, if you see the shipment appear in Shiptheory as "Not Ready", with the following message on the shipment activity notes:

This shipment is not ready for processing

This means that either the order has not been dispatched in ChannelGrabber, or the order in ChannelGrabber already has a tracking number. Shiptheory will not attempt to process any orders that already have tracking numbers.