If you see this error DPD Local Validation error (1030) The specified shipment date is in the past: collectionDate, the most likely reason is that the scheduling in your shipping rules is causing this. You can read about scheduling here to learn about it, if you're not already aware of what it is. By default any rules that are set to book in using our scheduling system and using any of the below terms will book in at midnight, and subsequently generate the error above.
To get around this you'll want to set a specific time as well, for example in the screenshot below, I have a set a time of tomorrow at 9am, this means the shipment will generate at 9am tomorrow rather than at midnight today and that will get around the error you've experienced.
If you need any help with this or have any issues, get in touch with support and we'll be happy to help!