Remote Desktop Connection can't connect....

Run this command elevated mode ob client computer.
reg.exe Add "HKCU\Software\Microsoft\Terminal Server Client" /V "RDGClientTransport" /T REG_DWORD /D "1"

or manually
HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client
Name: RDGClientTransport
Type: Dword
Data: 1

If this will not work ,you can always delete this entry. So do not hesitate.

Also a missing DLL file might cause this.

This wasn't the direct solution, but it lead me to the solution which was to edit a couple of registry keys.  I had edited them last week in advance of the PCI credit card requirement to use TLS 1.2.  As it turns out, my edits effected the ability to remote desktop as I had only enabled TLS 1.1 & 1.2  (apparently, 1.0 needs to be enabled, as well for RDC).  So, the registry key that I entered, 0x00000a00, had to be modified to be 0x00000a80 (per the table below).  Now RDC works, again, as before.

The DefaultSecureProtocols registry entry:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp
On x64-based computers, DefaultSecureProtocols must also be added to the Wow6432Node path:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp
The registry value is a DWORD bitmap. The value to use is determined by adding the values corresponding to the protocols desired.

DefaultSecureProtocols Value      Protocol enabled
0x00000008      Enable SSL 2.0 by default
0x00000020      Enable SSL 3.0 by default
0x00000080      Enable TLS 1.0 by default
0x00000200      Enable TLS 1.1 by default
0x00000800      Enable TLS 1.2 by default

https://support.microsoft.com/en-us/help/3140245/update-to-enable-tls-1-1-and-tls-1-2-as-a-default-secure-protocols-in