To mitigate a security vulnerability Microsoft implemented fundamental changes in the Credential Security Support Provider (CredSSP) protocol. RDP clients need to support the latest version of the the CredSSP protocol in order to use Network Level Authentication (NLA). It is therefore no longer possible to connect with older RDP clients.
openthinclient published the new version 2.1-1.2-36.4 of the FreeRDP packages, which supports the latest version of the CredSSP protocol. We advise all users to update the FreeRDP package.
More Information and a list of affected server systems: