Remote Desktop An authentication error has occurred (Code: 0×80070574).

I have to thank Morgan Che for posting this excellent article on fixing the An authentication error has occurred (Code: 0×80070574). 

Her post on http://www.vistax64.com/vista-networking-sharing/166833-problem-remoting-vista-enterprise-system.html 

In Remote Desktop Connection 6.0, server authentication verifies that you
are connecting to the correct remote computer or server, which may lead to
some incompatibility issue.
So, could you confirm if you use Remote Desktop Connection 6.0 client to
connect Vista?
Before Vista, Remote Desktop Connection 6.0 has been included in the
following OS:
Microsoft Windows Server 2003 with Service Pack 1 (SP1)
Microsoft Windows Server 2003 with Service Pack 2 (SP2)
Microsoft Windows XP with Service Pack 2 (SP2)
If so, please edit Default.rdp file as following steps to turn off the new
features in Remote Desktop Connection 6.0 to revert to the features in
Remote Desktop Connection 5.x.

To do this, follow these steps:
1. Click Start, click Run, type mstsc.exe, and then click OK.
2. Click Options, and then click the General tab.
3. Click Save As, and then type a file name in the File name box.
4. Select the location where you want to save the remote desktop file,
click Save, and then click Cancel.
Note The saved file has the .rdp file name extension.
5. Click Start, click Run, type notepad, and then click OK.
6. On the File menu, click Open.
7. In the Files of type list, click All Files.
8. In the Look in list, locate and then click the file that you saved in
step 4. Then, click Open.
9. Locate the line that resembles the following:
authentication level:i:n
Note The n placeholder represents the current authentication level.
10. Change the authentication level to 0 so that the line becomes the
following:
authentication level:i:0
Note When you set the authentication level to 0, RDP 6.0 does not check for
server authentication.
11. Add the following line to the end of the file:
enablecredsspsupport:i:0
Note When this line is present, you do not have to provide credentials
before you establish a remote desktop connection.
12. On the File menu, click Save.

More information, please see:
Remote Desktop Connection 6.0 prompts you for credentials before you
establish a remote desktop connection
http://support.microsoft.com/kb/941641
In addition, please also install hotfixs for Remote Desktop Connection 6.0
client, which can be achieved from:
Remote Desktop Connection 6.0
http://technet2.microsoft.com/window…-7038-4e82-a32
c-4bc10ffe56ab1033.mspx?mfr=true