How to Fix Error 721

So you use VPN(virtual private networking) and are trying to connect to another computer. Maybe it’s your work and you’ve been telecommuting in for a while, or you’re trying to connect to your home network from somewhere. Then it happens, you just can’t get connected and are getting error 721.
First Steps to Fix Error 721
There are several causes for this to happen. The first and most common is a firewall issue on the side of the computer you are trying to connect to, so we’ll address that first.
First you need to contact whoever is in charge of networking, like the IT department, for the computers you are trying to VPN into. Find out if they have made any changes to the firewall that could interfere with your connection. They should test to see if VPN traffic is passing through the firewall or if it is being stopped. If they see VPN traffic going through, the problem is on your computer.
Error 721 and Registry Errors
Like many errors, error 721 can be a registry error. A registry error is any problem with the core programming code that makes up your Windows operating system. Registry errors can be corrupt or missing files, links that point to nothing, or empty registry keys to name a few. Things like a slow computer, strange errors popping up, system crashes, hanging as programs load, and even the blue screen error can be traced to registry errors.
Steps to Take to Fix Error 721
I’m going to walk you through a system restore. It’s basically like taking your computer back in time to a date before you started getting error721. After we do the system restore, you will need to re-install any programs you installed between now and the date you pick.
For Windows Vista:
You want to restart your computer into Safe Mode. To do so, press the F8 button while your computer boots up until you get a menu. If your computer goes into Windows before you get the menu, you will need to try again.
Use your arrow keys to select Safe Mode from the menu
Press your Enter key
Once your computer is fully booted into Windows, you will see a pop up window informing you that you are in Safe Mode. Close the window
Go to your Start menu on the lower left of your desktop
Type “restore” in the search box. You will see system restore listed there. Click on that option.
You will have two options once you get into system restore. There will be a  recommended date and choose another date. You want to choose another date.
Look at the dates carefully, and pick one from before you started to get error 721, then click Next.
Click Finish
Reboot to normal Windows
Prevent Error 721
There is a way to prevent errors like error 721 from taking hold of your computer. There are programs called registry cleaners that are written for the express purpose of finding and fixing registry errors. If you get a good one and run it on a weekly basis it will make registry errors a thing of the past