If you’re having trouble using ZeroTier on Windows, the following steps may be of assistance.
Make sure you have Administrative Rights on your user.
Uninstall any other VPN software that could be conflicting with the ZeroTier setup.
Check for any antivirus software that has additional “Internet Security” features, that could be blocking installation and trying to assume Windows Firewall functionality.
Try different combinations of rebooting and reinstalling ZeroTier.
Side note: there were reported VPN issues in certain versions of Windows 10; those have their own fix via Microsoft.
If you continue to have issues, please check https://github.com/zerotier/ZeroTierOne/issues for any existing issues, or report a new one. Thanks!