"All TAP-Windows adapters on thsi system are currently in use."
To solve the issue, you need to re-enable the adapter or reinstall the driver.
Solution 1: re-enable the adapter
Open Control Panel > Network and Internet > Network and Sharing Center > Change adapter settings.
Check description of network adapters to find the Tap-Windows Adapter.
Right click on it > Disable.
Right click again > Enable.
Solution 2: reinstall the Tap driver
Check if it is already installed by opening C:\Program Files\TAP-Windows
Right click on Uninstall and select Run as administrator
Reboot the system (not required, but recommended) Download the Tap driver For Windows Vista,7,8
Download the Tap driver from OpenVPN repository and install it (right click on it > Run as administrator)