A few organizations have been stung with a interesting feature of the 2012 trial license.
When unlicensed, RDS 2012 will allow any version of the RDP client to connect. However once a license is activated, the server will only allow RDP 6.0+ clients to connect.
RDP 5 (Windowx XP SP2) and below clients will display a variation of the error “Remote Desktop disconnected because of a security error. The client cannot to the remote computer. verify you are logged on the network and try connecting again”
Why does RDS behave this way? This is undoubtedly a feature to enable testing in lab environments and should only impacts organizations with very old (i.e. 10 years old) thin clients.
What should I do if I’m affected by this? If you do get stung with this, its either time to flash / upgrade your thin clients or renew your thin client fleet with something from this era.