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nsdhouston asked on

Cisco VPN Client cannot connect - Error 51

I am unable to initialize the Cisco VPN client software on a Windows XP laptop.  When I click on the shortcut to intialize the program, it returns an error which reads:

"Error 51: Unable to communicate with the VPN subsystem
Please make sure that at least one network interface is active
and has an IP address and start this application again."

I have unintalled the client software and then re-installed, I have installed a newer version of the client software, and then uninstalled and re-installed the original version of the Cisco client software, and nothing has corrected this issue.

At one point in time, the client software ran perfectly on this laptop.  Without any knowledge of any changes to the system, it just started this error message a week ago and I cannot get around it.

Please advise on this - it is a critical issue dealing with a local law enforcement agency.

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Last Comment

8/22/2022 - Mon

Normally you would be right on track - more times than not, "VPN Subsystem" problems have to do with the vpn client software not properly communicating with the operating system.  Don't know if you're dealing with a "windows thing" or an environmental issue - firewall, etc.   Any software firewalls configured on the box that might be doing something weird? Any changes made to the system that you can tell us about?

Well, I gave up on this issue and decided to reload the laptop altogether.

I never was able to identify why the system started randomly having this problem and I experienced several other software related issues as I continued to troubleshoot the problem.

At the end of the day, it was easier to just reload the system and start from scratch.

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I have more or less the same problem.
Error 51 while I start the vpn client.
I have tried: Reinstallation, upgrade, downgrade, registry clean with WinTools.net Pro, TCPSock reset.

Helps nothing...
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James Murphy

Cisco VPN Client cannot connect - Error 51 any help

If you have McAfee firewall installed remove it. this is casued by third partry firewall.
Rajah - HORIBA

Thanks @ HoribaIT as a full reinstall of the OS was not required.
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