If an older version of Kerio was previously uninstalled, stale registry keys under the WOW6432Node path often conflict with new installations, causing a "device is already registered" block.

Before attempting to reinstall, you must ensure no trace of the old client remains.

Once the installation is successful, you can re-enable your security software. 4. Fix Windows Management Instrumentation (WMI)

If network connectivity is confirmed, the next suspect is a . Kerio Control updates often refine the VPN handshake. A client version 9.x attempting to connect to a server version 8.x may trigger Error 28201 because the cryptographic handshake fails. To resolve this, ensure both the client and server are updated to the latest compatible versions (e.g., both on the same major release). In some cases, the server configuration may have "Allow only secure ciphers" enabled, which the client cannot negotiate. The solution is to temporarily relax cipher requirements on the server for testing, then update the client.

Clear out any residual configuration data by navigating to the following path: HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Kerio Right-click the folder and select Delete . Step B: Uninstall Stale Network Interfaces Right-click the Start Menu and open the Device Manager . Expand the Network adapters category.