Multi-monitor configuration on shadower: “Shadow failed. Error code 120 (Error 120 – This function is not supported on this system.)”
When trying to shadow from one session to another session with a single monitor, shadowing works without issues, the error appears if the shadowee or shadower is using multiple monitors.
Note: The error is not explicit to this issue. This is a general error message that might occur in different scenarios.
Refer to Microsoft Article ID 2484290 for more information about session shadow with multiple monitors enabled in Windows Server 2008 R2.
Earlier to Windows 7 or Windows Server 2008 R2, there is no built-in support for multiple monitors in Remote Desktop sessions. With the introduction of multi monitor support in Remote Desktop Services, shadowing is now depending on underlying functionality available in operating system.