License Issue after upgrade to OS Deployer 4.0

Hello there, we've recently upgraded from OS Deployer 3 to version 4. We currently have 40 OS Deployer 3.0 for workstation machine licenses. But now when I try to deploy an image to a machine using PXE boot I get the following error:

Host '<ip>' has failed the deployment.
Additional info:
--------------------
Error code: 1
Module: 52
LineInfo: 9C5A16066A60D516
Fields: $module : "C:\Program Files (x86)\Common Files\ManageEngine\Agent\osd_server.dll"
Message: Host '<ip>' has failed the deployment.
--------------------
Error code: 2
Module: 100
LineInfo: 876D9AA543F78D10
Message: No ManageEngine OS Deployer 4.0 for Workstation - Machine License on '<ip>'.

I'm guessing that this error is occuring because we don't have any OS Deployer 4.0 workstation licenses. Does this mean that our 40 unassigned OS Deployer 3.0 workstation licenses are now useless? Is there a way to cash them in, or change them into 4.0 licenses?

Thanks in advance for your assistance.