I have been getting something like this for a few days now. I can get the Avis website to work, but the moment I sign in to my account I get an error. Can’t make any bookings at all.
ADDED: I have tried deleting all cookies and history, using a different machine from a different IP, using a VPN in a different country, using different browsers, using the iPhone app. Nothing makes any difference. I made two bookings by phone yesterday and the agent said they could see nothing strange marked on my account.