I have several people who connect to our company VPN from home with Windows XP PRO SP2. After these users bought new pc loaded with Vista Home Premium SP1, they can no longer connect to our company VPN. I thought that it had something to do with the version so I upgraded the pc to Vista Business SP1 with the same VPN error. The remote users are connecting to the Internet fine through either Comcast or Verizon. But when they try to connect to the VPN, they get the message Error 800: VPN connection could not be established. After setting up a Vista Business SP1 at my home to check the problem, sure enough Im getting the same error. I have both my Windows XP Pro SP2 and Windows Vista Business SP1 hard wired to a 3com wireless router. My DSL modem has the firewall set to allow all traffic. I disabled the firewall on my 3com wireless router. I disabled the Vista firewall and Defender and still getting the same error. My Windows XP Pro SP2 with the firewall turned on is working just fine. Any suggestions? Thank you in advance for your help.

Maybe the VPN client that you are using is not compatible with Vista. I had the same problem with my new laptop. We use a Cisco VPN connection and it did not work with Vista. We contacted Cisco and got a more current version of the VPN client and configured the firewall to allow the connection and it worked. What VPN client are you using?

Our VPN server is a Cisco 1800 series. As far as the VPN client? I'm basically going to Network and Sharing Center and setting up a VPN connection to your workplace using my existing Internet connection. Are you suggesting that I install a third party VPN client. Please crarify. I never had to do that with XP pro. Thank you.

You might have too with Vista. I had to install the Cisco VPN client connector for mine to work.You also might want to consider disabling IPv6 as well. I have ran into problems with that protocol before.Go to Control Panel > Network Sharing Center > Manage network connections > and right click the connection you want to edit and select properties and disable IPv6. That might even fix your VPN problem without having to install the VPN client. However if it does not work, I would contact Cisco and see if they can help you troubleshoot the connection. They might have a client software you can install to force the connection through.Let me know how it works out.

I had the same problem with Vista Home Premium SP1 when using the Windows VPN client, but I was able to resolve it by specifying the DNS server address. Follow this general path to specify the DNS server address (I'm in front of an XP machine as I write to the path may be off by a bit): Network Connections > [desired connection name] > Properties > TCP/IP v4 (can't remember the exact wording) > Properties > General > Advanced > DNS > Use the following IP address This allowed for a successful VPN connection to my corporate network; however, once the connection was established, my machine could not be registered on the network and failed with error 742. I was able to resolve this issue by (carefully) modifying my registry to support weak encryption with a solution that I found on the MS support forums (see the article in the link below). Since I made both of these changes, my VPN issues have been resolved. I hope this helps. I went back and forth with MS for three months before I found the solution myself. Good luck! http://support.microsoft.com/kb/929856