This solution comes from: http://www.tek-tips.com/viewthread.cfm?qid=1225579&page=1

Windows XP with SP2.  IBM T43, actually.  The problem materialized after I did a driver update (ThinkVantage Software Installer) and rebooted the system.  Running F-Secure Client Security 6.01.

Error 720: A connection to the remote computer could not be established.  You might need to change the network settings for this connection.  (See screenshot below.)

I had confirmed that PPTP was properly selected as VPN type (VPNing into ISA 2004 with latest service pack via RRAS).

1. As per 810979, navigate to the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}
2. Do a backup of the key and all children, then find the WAN Miniport (IP) and delete the key.  I ended up flushing out all other protocols listed here as well.  (ie. Deleting all the keys).
3. Now, journey into Device Manager, and select Show All Hidden Devices.
4. Under Network Adapters, nuke all the WAN Miniports.
5. I removed my network adapters (wired and wireless) for a good measure.
6. Restart the system
7. Fire up notepad and open c:\windows\inf\netrasa.
8. Comment out (shove semicolons in front of) the lines starting from "Excludefromselect=\" and ending with "MS_NdisWanNbfIn,MS_NdisWanNbfOut" under the [ControlFlags] section.  This allows the WAN Miniports to be reinstalled manually.
9. Now, reinstall the WAN Miniports.  Go into Add New Hardware in Control Panel.  Choose a specific hardware device, Network Adapters, and select Microsoft as the manufacturer.  Find all the WAN Miniports (PPPoE, PPTP, IP, et al... whatever you removed previously) and add them one at a time.
10. Next, reset the TCP/IP stack as per 299357.  I did "netsh int ip reset c:\resetlog.txt"  I stumbled on some other VB apps, but they didn't seem as trustworthy =).
11. Enjoy the VPN.