source: https://vpn.ac/knowledgebase/64/OpenVPN-Error-All-TAP-Windows-adapters-on-this-system-are-currently-in-use.html

The error message "All TAP-Windows adapters on this system are currently in use" indicates an issue with the virtual Tun/Tap network adapter, which is crucial for OpenVPN operations on Windows. Here's how to address this problem:

Step 1: Re-enable the TAP-Windows Adapter

1. Navigate to the Control Panel, select "Network and Internet," then go to "Network and Sharing Center" and click on "Change adapter settings."
2. Look through the list of network adapters to locate the TAP-Windows Adapter.
3. Right-click on the TAP-Windows Adapter and select "Disable."
4. Right-click on it again and choose "Enable."

Step 2: Reinstall the TAP Driver

1. Go to C:\Program Files\TAP-Windows to check if the TAP driver is installed.
2. Find the uninstaller, right-click it, and choose "Run as administrator."
3. Although it's optional, restarting your computer is recommended.
4. Download the latest TAP driver from the OpenVPN repository (example: https://swupdate.openvpn.org/community/releases/tap-windows-9.21.2.exe)
5. Right-click the downloaded installer file and select "Run as administrator" to install the driver.