I am using the Windows 7 x64 default IE8 which is IE8-32 bit. I do not use the IE8 x64 version.
On 23-October-2009, I upgraded from Vista SP2 x64 Business to Windows 7 x64 Professional and it is latest version of Windows 7. All updates from Windows Update were also installed after the initial Win 7 upgrade.
I am reasonably confident that the Avira login worked under Vista SP2 x64 Business and with V188.8.131.52 of SP. The issue with Avira user forum and also the issue with TrojanHunter forum started after V184.108.40.206. I have been running SP V4 betas for approximately 10 months. In fact, I purchased a V4 license on 26-December-2008, shortly after I upgraded from Vista 32-bit to Vista 64-bit. Prior to that I was using V3.x.
I hope this helps.
Windows 8.1.1 x64 Pro on Dell XPS 8700 SE, IE 11 with 2 Samsung 850 Pro SSDs, 3 monitors, ASUS RT-AC68R rtr; WD My Cloud ext drive, MS Surface Pro tablet & Dell XPS 410 with Windows 10 x64. MS Office 2013, Avira IS Pro 2015, MBAM, MBAE, SAS Pro.