How to Solve VPN Error Code 51 on Windows PC


VPNs are used for protecting yourself from any cyber threats and ensure your privacy over the web. Even if they are designed for easing our life and they mostly do this for us, they may have some errors on Windows. There are plenty of different error codes on VPN, however, in this article, we will focus on VPN Error Code 51 on Windows and possible solution techniques to solve Error Code 51.

What is VPN Error Code 51 on Windows?

“Unable to communicate with the VPN subsystem. Please make sure that you have at least one network interface that is currently active and has an IP address and start this application again.”

This is generally related to a fundamental connection problem and your network has stuck. You need to restart your VPN and remove the problems that may cause this lock-up of the network.  If you use a VPN  for Windows and the error code 51 has popped on your screen and you are unable to proceed to your VPN connection, make sure that you read below to find out what is the reasons and solutions for VPN error code 51.

What are the causes of VPN Error Code 51?

There are several probable causes mentioned by both Windows users as well as VPN customers stated. We will dwell on mostly discussed Error 51 code causes and their solutions.

1. Cisco VPN Generated Error

This code is generally encountered with Cisco VPN clients. In short, the Error Code 51 means that your VPN cannot establish a connection with the VPN server. The problem is about the software that is used in the infrastructure of the Cisco VPN server. The connection cannot go through a software network.

To solve the Cisco VPN Error 51 Code, close your VPN and try to determine problems with the network diagnostics. Restart the VPN again. This method will solve your issue most of the time.

2. Error Code 51 with Multiple VPN Services

Having multiple VPN clients installed on your computer can easily cause connection blocking. The solution is simple. Choose the VPN client you want to use, uninstall the other one and then, restart your computer.

We may recommend uninstalling and reinstalling the VPN client you chose one more time.

3. VPN Blockage by the Firewall Causing Error Code 51

Since the firewall of your device tries to protect the main system and maintain its operation, problems caused by firewall restrictions are observed with many external software usages including using VPN. While it tries to monitor all traffic coming and going, may cause unspecified errors that will lead to connection problems of VPN.

To solve this issue, you can disable your Firewall for a moment. To do this you should open Windows defender and disable the following features of Firewall activity.

Turn off your Windows Defender for domain network, public network, and private network.

4. VPN Blockage by Antivirus Application Causing Error Code 51

Just like the firewall, Antivirus programs work for the same logic and act more meticulously to detect malicious software. This tendency may cause blocking of VPN connections from time to time.

Especially if you use VPN to safely browse certain websites and download files, an antivirus program will detect these dangerous files or website cookies and associate this threat with the VPN. Hence, it will cause Error code 51 on your VPN due to the threats detected by antivirus software.

To detect this, you may try to disable your antivirus program to check whether the problem continues.

If it is really about the Antivirus software, then you make sure to adjust the settings of your antivirus program, look at the things that the program allows or restricts.

If the problem still continues, you may choose to go with the Windows Defender rather than Antivirus since it may overcontrol the Windows system’s firewall as well and this may cause the Error Code 51 on your VPN connection problem.

5. Router Problems causing Error Code 51 on VPN

Maybe there is a deeper program rather than just the programs on your computer. Your router may not successfully initiate the connection with the server.

Router problems likely to cause multiple and sudden connection drops while using a VPN. However, some well-known VPNs may prevent this and can provide a seamless connection thanks to its technical features.

To assess this issue, if you are out of the options stated above, disable your router, and connect to the internet via an ethernet cable. This will show whether the Error Code 51 problem is caused by the router.

Solutions for Router Problems Triggered Error Code 51

Firstly, try to reboot your router, maybe several times. Your router may have to experience setbacks due to multiple operating systems if they are installed on your device.

Try to close other devices that may create overwhelming demand on the router.

Apply the following method for the restart of your router:

Press for 30 seconds on the router’s reset button, stay disconnected for 30 more seconds, and then by pressing for 30 seconds more try to open it.

6. Too Many Users on the VPN Server

If you are using a free VPN or maybe in a busy time of the day or busy server location, too many requests on a VPN server may cause connection disruptions and hence cause Error Code 51.

To examine this problem, you can utilize a ping test. If you cannot achieve a result, consider switching to another server. If you use high-quality VPNs, they usually provide a live statistics dashboard to show traffic, server density, and capacity.

For the Cisco VPN client, after checking all possible reasons like an antivirus program, firewall program, router connection, reinstalling your Cisco VPN client, and consequently your device is needed.


To avoid VPN connection problems like VPN Error Code 51 on Windows, in the beginning, when you configure your VPN client for the device, pay attention to settings that will not clash with your firewall or antivirus program. The same applies to the firewall and antivirus program settings as well, even more. Your antivirus programs may throw unrelated threats and disable VPN connections if the settings are configured in that way.