After configuring DirectAccess in an IPv4-only deployment with a single network adapter, and after the default DNS64 (the IPv6 address which contains ":3333::") is automatically configured on the network adapter, attempting to enable load-balancing via the Remote Access Management console causes a prompt for the user to supply an IPv6 DIP. If an IPv6 DIP is supplied, the configuration fails after clicking Commit with the error: The parameter is incorrect.

Download the backup and restore scripts from Back up and Restore Remote Access Configuration.
Back up your Remote Access GPOs using the downloaded script Backup-RemoteAccess.ps1
Attempt to enable load balancing until the step at which it fails. On the Enable Load Balancing dialog box, expand the details area, right-click in the details area, and then click Copy Script.
Open Notepad, and paste the contents of the clipboard. For example:
Set-RemoteAccessLoadBalancer -InternetDedicatedIPAddress @(‘10.244.4.19/2 55.255.255.0′,’fdc4:29bd:abde:3333::2/128’) -InternetVirtualIPAddress @(‘fdc4:29bd:abde:3333::1/128’, ‘10.244.4.21/255.255.255.0’) -ComputerName ‘DA1.domain1.corp.contoso.com’ -Verbose
Close any open Remote Access dialog boxes and close the Remote Access Management console.
Edit the pasted text and remove the IPv6 addresses. For example:
(Remove de IPv6 IP Addresses)
Set-RemoteAccessLoadBalancer -InternetDedicatedIPAddress @(‘10.244.4.19/2 55.255.255.0’) -InternetVirtualIPAddress @(‘10.244.4.21/255.255.255.0’) -ComputerName ‘DA1.domain1.corp.contoso.com’ -Verbose

In an elevated PowerShell window, run the command from the previous step.
If the cmdlet fails while it is running (not due to incorrect input values), run the command Restore-RemoteAccess.ps1 and follow instructions to make sure that the integrity of your original configuration is maintained.
You can now open the Remote Access Management console again.