It may require you to re-validate your License Agreement with WAIK / WADK.
Try this command on the LDMS database to reset the flag and re-activate the button under "Validate Licenses" in the Operating System Deployment module.
UPDATE [LDMS90].[dbo].[KeyValue] SET intvalue = 0 WHERE ApplicationName = N'WAIKLicenseAgreement'
Has to be done from the core server, sorry for the delay in response.