How To Fix RDP Authentication Error due to CredSSP

The error will show the below text

An authentication error has occurred.
The function requested is not supported
Remote computer:
This could be due to CredSSP encryption oracle remediation.

What Caused The Issue?

In March 2019 Microsoft released an update to windows 10 which addressed vulnerabilities for the Credential Security Support Provider protocol which is used by Remote Desktop Protocol.  This in turn caused issues when trying to RDP to machines. For more information on this update click here
This update apply’s a new encryption oracle remediation policy setting on the server or client which requires you to connect via a secure RDP session.
There are a few ways that you can resolve this issue, The easiest to implement is to add a registry entry on the machine you are trying to connect from which I will show you below.

How To Fix RDP Authentication Error due to CredSSP

To Fix RDP Authentication Error due to CredSSP do the following

1. Click start, type in regedit and hit enter
2. Navigate to HKEY_LOCAL_MACHINE > SOFTWARE > Microsoft > Windows > CurrentVersion > Policies > System > CredSSP > Parameters
3. Double click on AllowEncryptionOracle
4. In the value data field enter 2
5. click ok
6. Close down the registry editor
7. Try to connect to the client again

If you still get the same error continue with the next fix.

Fix 2 : Edit Local Group Policy

There is a setting in the local group policy which will also resolve this error.  The advantage of applying this fix is that it will apply to all users of the system.
To apply this fix follow these steps

1. Click start and type in gpedit.msc and hit enter
2. Browse to Computer Configuration > Administrative Template > System > Credentials Delegation
3. Double click on Encryption Oracle Remediation
   
4. In the next window, select enabled and protection level = Vulnerable
5. Click ok to close gpedit
6. Try to connect to the client againIf you still get the same error continue with the next fix.