I've been getting an error that has been bugging me recently on my Windows 10 device - a Surface Pro 4 running the Fast Ring Insider build (at this time its Build 14342_rs1_release.160506-1708).
Trying to Remote Desktop to a Windows Server 2008 just wouldn't work -- not matter what combination of credentials I tried, it just failed with a 'Login Failed' error. Oddly, connections to other machines running Server 2012 DID work. I shrugged it off and ignored it until I got time to look at it today - and the fix amazes me.
Simple enable the Firewall exception for Remote Desktop -- fire up firewall.cpl, click allow a program through the firewall, and select Remote Desktop. Reboot, and that's it.
Must be something getting blocked around the authentication or such. But at least that's working again.