Viscosity comes inbuilt with TUN/TAP drivers that allow your VPN connection to be created. However if Viscosity is unable to load these drivers you may see an error like "Cannot allocate TUN/TAP dev dynamically" in the OpenVPN log.

In most instances this error is caused by Viscosity having incorrect permissions. This can usually be solved by making sure Viscosity is installed in your Applications folder. Viscosity is unable to correctly run from some locations (such as your Downloads folder, or your Home directory if FileVault is on). Viscosity can be moved to the Applications folder like so:

1. Quit Viscosity if it is running.
2. Drag the Viscosity application to your Applications folder.
3. Open your Applications folder and double-click on Viscosity to start it.
4. You may be asked for an Administrator's username and password if Viscosity has detected its permissions needed updating.

If Viscosity is already installed in your Applications folder, try re-installing the latest version of Viscosity. This can be done like so:

1. Quit your old copy of Viscosity if it is running.
2. Move your old copy of Viscosity to the trash.
3. Download Viscosity from the Viscosity website.
4. Open the Viscosity.dmg file in your Downloads folder.
5. Drag Viscosity to your Applications folder.
6. Eject the Viscosity disk image.
7. Launch Viscosity from your Applications folder.

If you are still getting the error, it's possible that other VPN clients (such as Cisco AnyConnect) may be interfering with Viscosity's TUN/TAP drivers. If you have any such clients installed, try temporarily quitting and/or uninstalling them to see if that solves the problem.

Finally, it's possible there may be a temporary conflict. Try restarting your computer and connecting Viscosity again.