If you're getting an error that says you're unable to print your Parcelforce label, as per the below image, please check that the shipment was only created today.

For instance, if the shipment was created on 21st of November it means that you can only print it on the 21st. If you try to print it in the 22nd, you'll get an error. If a shipment is not printed on the day it was created it is automatically deleted overnight.