Problem Solved :-) Solution install an older version of Himachi like V 328.
Network Type - Gateway
Problem - message "Failed to connect to the network adapter. Peer is not accessible via VPN" started appearing on a number of cleint PC's on the network. These were working fine in the past.
Tried various options over 3 days, including removing drivers, uninstalling, reinstalling, removing firewall etc, nothing worked.
Solution - install Himachi - version 328, it works !!!
Step by Step Process;
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1. Download Himachi version 328, from file sharing site like filehippo etc.
2. Warning - before installing Himachi - make sure to disable internet access (otherwise the version is automatically updated).
3. Disable Internet access
4. Install Ver 328
5. Start Himachi -> System -> Preference -> Settings -> Disable Automatic Updates.
6. Enable Internet access
7. Connect to network
It shown now work :-)