The error "All TAP-Windows adapters on this system are currently in use"
suggests that there is a problem with the virtual Tun/Tap network
adapter used by OpenVPN on Windows. 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
Download the Tap driver from OpenVPN repository and install it (right click on it > Run as administrator)
If
you don't have access to openvpn.org but you have our software, open
our software location (where it was unzipped) and find the driver in the
data\Tap\ subfolder.
