Why this happens, I don't know but there are 2 steps needed to resolve this..
1.ENABLE LOGIN AGAIN
Open RD Connection and select options and save as - I find broken.rdp on desktop to be a useful filename.
Open broken.rdp with notepad and append the following line..
enablecredsspsupport:i:0
Then you can login again by using broken.rdp ( double click it from the desktop )
2.CHECK YOUR DOMAIN
An interesting part of the problem for me is that I now get the message password is incorrect. Why? Because in my case I needed to specify the correct domain. In this case my computer is not on a domain. So, I had to specify the username as..
computername/username
Unlike many responders on this site, I am answering as a user who has experienced this problem many times and resolved it many times with this technique.