Remmina allows to connect to computers via different protocols (NX, RDP, SFTP, SSH, VNC and even XDMCP). Microsoft Windows allows remote control of a computer via RDP (Remote Desktop Protocol). Some Windows Updates in March, 2018 may break connectivity via Remmina, which uses FreeRDP to connect to Microsoft Windows machines. This is not an issue with FreeRDP, but with some implementation or modification on Microsoft's side, which tries to only allow machines within the domain to use RDP to communicate with each other.
There is a simple fix for this. Follow these steps:
1) Connect to the Microsoft Windows machine via RDP from another Microsoft Windows machine using "Remote Desktop Connection" by typing mstsc in the "Start" menu and typing either the computer name or its IP address. Use proper credentials
2) Right click on "Computer", "My PC" or "This PC" and click on "Properties"
3) Click on "Change settings"
4) Click on the "Remote" tab
5) Uncheck the "Allow connections only from computers running Remote Desktop with Network Level Authentication (recommended)"
6) Open "Services" by typing services.msc in the "Start" menu
7) Restart "Remote Desktop Services" by right clicking on it and clicking on "Restart"
Note: This last step will disconnect the RDP session
8) Attempt connection to machine again after 15 to 30 seconds
1) Right click on the machine name from step 1) in the Microsoft Windows section
2) Click on "Edit"
3) Click on the "Advanced" tab
4) Change "Security" to "RDP"
Note: Option "NLA" for "Network Level Authentication" may not work, neither does option "Negotiate" (default)
5) Click on "Save"
6) Double click on machine name to attempt connection, which should be successful
F. Bobbio C.