edit - as of Feb 8th 2019, any appliances which still had update01.barracudanetworks.com in their NTP server list have been automatically updated to use ntp.barracudacentral.org instead, which is an alternative NTP server controlled by Barracuda Networks. This does not affect customers who have already configured their own NTP infrastructure, or those who have moved to the NTP pool, only customers whose appliances still referred to the now-defunct update01 server. Original text follows...
Unfortunately the Barracuda-provided NTP services at update01.barracudanetworks.com are currently unavailable. It has come to our attention that some SSL VPN appliances may still be configured to use this server for NTP time - this is not a recommended configuration as it is only available in the US and best practice is to use local NTP services for more consistent timekeeping, but not all customers will have changed the default settings.
We recommend that any customers who haven't already configured their own NTP settings take this opportunity to do so - if you have on-premises NTP servers, then you should use those where possible. If you do not, then the quickest solution is to use a server from the NTP pool based in your region. Available regions are:
This can be done by accessing the appliance UI on your SSL VPN (port 8000 HTTP, port 8443 HTTPS) and configuring the NTP server list on the Advanced->Advanced Networking tab. Please bear in mind that this is particularly important if you are using Google Authenticator, because if the clock on your SSL VPN appliance drifts more than 30 seconds away from the clock on a mobile device, the user will be unable to login because the two devices will not be generating matching codes.
Apologies for the inconvenience.