Our client have recently upgrade the security protocol to TLS 1.2. Therefore We have our application upgraded to 4.6.1 expecting the security protocol will be default to TLS
I had a similar problem and this is what worked for me.
open Powershell and check for supported protocols by using [Net.ServicePointManager]::SecurityProtocol
Run the following 2 cmdlets to set .NET Framework strong cryptography registry keys:
set strong cryptography on 64 bit .Net Framework (version 4 and above)
Set-ItemProperty -Path 'HKLM:\SOFTWARE\Wow6432Node\Microsoft\.NetFramework\v4.0.30319' -Name 'SchUseStrongCrypto' -Value '1' -Type DWord
set strong cryptography on 32 bit .Net Framework (version 4 and above)
Set-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\.NetFramework\v4.0.30319' -Name 'SchUseStrongCrypto' -Value '1' -Type DWord
Restart Powershell and check again for supported protocol by using [Net.ServicePointManager]::SecurityProtocol
It should now display Tls12 as well.
Hope this helps