You see Error 734: The PPP link control protocol was terminated when connecting to a VPN, especially one using multi-factor authentication (MFA). This indicates the Point-to-Point Protocol (PPP) negotiation failed, often during the MS-CHAPv2 handshake with MFA.

The Fix

Apply these fixes in order. Test your VPN connection after each step.

First, adjust the VPN connection's security settings. This is the most effective fix for MFA-related Error 734.

1. Open Control Panel > Network and Sharing Center > Change adapter settings.

2. Right-click your VPN connection and select Properties.

3. Go to the Security tab.

4. Set Type of VPN to match your server (often Automatic or PPTP).

5. For Validate my identity, select Allow these protocols.

6. In the list below, check only Microsoft CHAP Version 2 (MS-CHAP v2).

7. For Data encryption, try Optional encryption first. If it fails, change it to Require encryption.

8. Click OK and attempt to reconnect.

If that doesn't work, disable multi-link negotiation.

1. In the VPN connection's Properties, go to the Networking tab.

2. Click Configure... next to your modem or adapter.

3. Uncheck the box for Negotiate multi-link for single link connections.

4. Click OK twice and test the connection.

If that doesn't work, clear saved credentials and reset the network stack.

1. In the VPN Properties, go to the Options tab and ensure Remember my credentials is unchecked. Re-enter your credentials on the next connection attempt.

2. Open an elevated PowerShell or Command Prompt window and run these commands:

netsh int ip reset
netsh winsock reset
ipconfig /flushdns

3. Restart the computer.

If that doesn't work, check for interference and update drivers.

1. Temporarily disable third-party firewall and antivirus software.

2. Update or reinstall the drivers for your network adapter via Device Manager.

Verify

If the client-side fixes do not resolve Error 734, the issue is likely server-side. The VPN server configuration must be compatible with PPP-based protocols (PPTP, L2TP) and MFA. Common problems include MFA token timeouts that exceed PPP's MS-CHAPv2 negotiation window or a server configured to reject MS-CHAPv2. Contact your VPN administrator to verify the server's PPP authentication settings. For advanced debugging, enable PPP logging by setting the DisablePPPLogging DWORD to 0 in the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings and review the logs in Event Viewer under Windows Logs > System (source RasMan).

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