You receive the error "The remote server returned an error: (401) Unauthorized" when attempting to download a package from the Package Library.
Make sure you have the proper firewall exceptions in place to allow the package to download to your PDQ server. Check out this article: Windows Firewall Ports and Exceptions under the External Exceptions section and make sure you can get to those sites. Please attempt the download again once you've applied the new firewall rules.
We also see this error occur when an account change has been made that generates a new license, causing the currently applied license to be invalidated even if the expiration has yet to be reached. When an account change occurs, an email will be sent to both the primary contact and the technical contact on your account with the new license keys. If you are unable to find an email with the updated license keys, login (or create a login) on our sales portal site: https://sales.pdq.com/opt-in, using the current Technical or Billing email account for your organization. You should then be able to retrieve your latest license keys.
On your PDQ Server, for both Deploy and Inventory, navigate to Help > License > Enter a New License and paste the new license keys. Close PDQ Deploy and PDQ Inventory and then restart both PDQ services (using services.msc) or simply reboot the PDQ server and try the download again.