This is caused by faulty Windows programming or a corrupted version of OpenVPN.
Please ensure you are using the latest version of OpenVPN which is 2.1.1 which has full Vista/7 support.
If you still have problems (for Vista/Windows 7 only),
1. Go to C:\Program Files\OpenVPN\bin\
2. Right click openvpn and in compatibility mode select Run as Administrator.
3. Do this for openvngui as well.
4. Exit openvpn and then open it up again.
If that still doesn't work (for all Windows versions):
Easy way1. Right click on OpenVPN GUI task icon in the bottom right hand corner of your start bar.
2. Left click on Edit Config
3. Insert the following statement on a new line after 'proto udp'
ip-win32 netsh
4. Restart OpenVPN
Alternate way if above does not work1. Click on Start, Go to Run
2. Type services.msc
3. Find DHCP Client
4. Right click and restart the DHCP Client
5. Restart OpenVPN
Another thing to try:
1. Open up your desired .ovpn file (config file found in C:\Program Files\OpenVPN\config)
2. Add the following lines after 'cipher none'
route-method exe
route-delay 2
3. Save.
4. Reconnect.
And if all the above does not work1. Uninstall OpenVPN
2. Reinstall OpenVPN