I am using latest Windows 10 on a ThinkPad X1 to access latest Windows 7 on a desktop. Previously everything worked fine. That was with 6.5.x on both. Yesterday I updated the client to 6.6.8, rebooted, and everything seemed to still work properly. Today I updated the Windows 7 server with 6.6.8, and rebooted it, and then when I tried to connect, I got a screen that was mainly green, along with the windows menu bar on the top of the screen rather than the bottom.
I seem to have been able to get it to work by selecting display options and checking most of the boxes to disable things, but that was never needed before.
Again, this is with the free version 6.6.8, 64 bit Windows (10 on client, 7 on server).