There is a problem with your Remote Desktop license, and your session will be disconnected in 60 minutes. Error in RDS workgroup environment

You receive error. 

There is a problem with your Remote Desktop license, and your session will be disconnected in 60 minutes. Contact your System Administrator to fix this problem.

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Only Per Device remote desktop licenses are supported in a workgroup environment.

Change the remote desktop licenses to Per Device. This can be done in Remote Desktop License manager by right-clicking the Per User licenses and choosing to convert to Per Device. 

If Per User licenses are required, then a domain must be created and all the servers joined to the domain.

In a workgroup environment, the license mode of the server should be set to 2 for Per Device and the license server name should be configured to allow remote desktop licenses to be issued.

This can be configured in the following registry locations by going to Start > Run then type regedit then press enter.
 

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\Licensing Core
DWORD LicensingMode

4 = Per user
2 = Per Device

The license server can also be set through the registry here:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TermService\Parameters\LicenseServers

REG_MULTI_SZ SpecifiedLicenseServers = Servername