Recent Windows updates (e.g., version 2004 and later) require strictly signed drivers. Older Kerio versions may lack these signatures, triggering a block.

An outdated Kerio client installer is incompatible with a recent Windows security update. Step-by-Step Solutions to Fix Error 28201

Error 28201 is a specific error code associated with the Kerio VPN Client. When this error occurs, the client software is unable to establish a connection to the Kerio VPN server, displaying an error message: