SSL VPN login denied from Mac Clients

Hello,

I'm encountering a problem with a Sophos SG230 (Firmware version 9.702-1) and Mac Os clients (with Tunnelblick or Viscosity as VPN client).

The problem is the same reported here:

https://community.sophos.com/kb/en-us/127843 (Sophos XG Firewall: SSL VPN client, Tunnelblick 3.7.4a fails to connect).

Same error: format error in cartificate's notBefove field

I'm using the last version of Tunnelblick (3.8.2) and this version works perfectly on the other 2 Firewall of mine.

It can't be caused from a mistyping error: under Windows everything works.

On this firewall are present 2 kinds of users, remotes (from an old and often unreachable Domain Controller) and locals. I've tested only locals users.

Anyone have an idea?

Thanks