Hi Bonnie,
if the web site is intentionally blocking an access from the VPN gateways, the options are either to contact the website support and convince them to modify the rules, or to disable the VPN for the time when you are accessing the web site. There's planned an update of the Smart VPN mode of Avast SecureLine, in which you could whitelist the web as trusted to disable the VPN automatically for you.
Best Regards,
Martin