So far I have configured a firewall rule between both sites that enables access via all the ports listed on; have uninstalled the client, rebooted and reinstall, but no luck there either.
Quite possibly I am missing something really silly, but I just can't figure this one out.
Kaspersky bills itself as one of the strongest anti-virus software programs available, but if you can't download the automatic database updates from Kaspersky, you won't be able to protect your computer from threats like viruses and malicious software.
This can be a downward spiral, since an outdated database makes your computer more vulnerable to attack from new viruses or malware, which can further prevent you from downloading new updates from Kaspersky.
For example, when you install Kaspersky on your computer, it automatically disables any Microsoft Windows firewalls already installed and uses its own.